Amino acid transporters and uses

ABSTRACT

The present invention relates to novel mammalian amino acid transporter proteins and the genes that encode such proteins. The invention is directed toward the isolation, characterization and pharmacological use of the human amino acid transporter proteins EAAT1, EAAT2, EAAT3 and ASCT1. The invention specifically provides isolated complementary DNA copies of mRNA corresponding to each of these transporter genes. Also provided are recombinant expression constructs capable of expressing each of the amino acid transporter genes of the invention in cultures of transformed prokaryotic and eukaryotic cells, as well as such cultures of transformed cells that synthesize the human amino acid transporter proteins encoded therein. The invention also provides methods for screening in vitro compounds having transport-modulating properties using preparations of transporter proteins from such cultures of cells transformed with recombinant expression constructs.

This application is a divisional of U.S. Ser. No. 09/042,929, filed Mar. 17, 1998, which is a divisional of U.S. Ser. No. 08/546,666, filed Oct. 23, 1995, now U.S. Pat. No. 5,776,774, which is a divisional of U.S. Ser. No. 08/140,729, filed Oct. 20, 1993, now U.S. Pat. No. 5,658,782, issued Aug. 19, 1997. The disclosures of each of these prior applications are considered as being part of the disclosure of the application and are explicitly incorporated by reference herein.

This invention was made with government support under National Institute of Health grants DA07595 and DA03160. The government has certain rights to this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to amino acid transporters from mammalian species and the genes corresponding to such transporters. Specifically, the invention relates to the isolation, cloning and sequencing of complementary DNA (cDNA) copies of messenger RNA (mRNA) encoding each of four novel human amino acid transporter genes. The invention also relates to the construction of recombinant expression constructs comprising such cDNAs from each of the four novel himan amino acid transporter genes of the invention, said recombinant expression constructs being capable of expressing amino acid transporter proteins in cultures of transformed prokaryotic and eukaryotic cells. Production of the transporter proteins in such cultures is also provided. The invention relates to the use of such cultures of such transformed cells to produce homogeneous compositions of each transporter protein. The invention also provides cultures of such cells producing transporter proteins for the characterization of novel and useful drugs. Antibodies against and epitopes of these transporter proteins are also provided by the invention.

2. Background of the Invention

The approximately 20 naturally-occurring amino acids are the basic building blocks for protein biosynthesis. Certain amino acids, such as glutamate and glycine, as well as amino acid derivatives such as γ-aminobutyric acid (GABA), epinephrine and norepinephrine, and histamine, are also used as signaling molecules in higher organisms such as man. For these reasons, specialized trans-membrane transporter proteins have evolved in all organisms to recover or scavenge extracellular amino acids (see Christensen, 1990, Physiol. Rev. 70: 43-77 for review).

These transporter proteins play a particularly important role in uptake of extracellular amino acids in the vertebrate brain (see Nicholls & Attwell, 1990, TiPS 11: 462-468). Amino acids that function as neurotransmitters must be scavenged from the synaptic cleft between neurons to enable continuous repetitive synaptic transmission. More importantly, it has been found that high extracellular concentrations of certain amino acids (including glutamate and cysteine) can cause neuronal cell death. High extracellular amino acid concentrations are associated with a number of pathological conditions, including ischemia, anoxia and hypoglycemia, as well as chronic illnesses such as Huntington's disease, Parkinson's disease, Alzheimer's disease, epilepsy and amyotrophic lateral sclerosis (ALS; see Pines et al., 1992, Nature 360: 464467).

Glutamate is one example of such an amino acid. Glutamate is an excitatory neurotransmitter (i.e., excitatory neurons use glutamate as a neurotransmitter). When present in excess (>about 300 μM; Bouvier et al., 1992, Nature 360: 471-474; Nicholls & Attwell, ibid.; >5 μM for 5 min.; Choi et al., 1987, J. Neurosci. 7: 357-358), extracellular glutamate causes neuronal cell death. Glutamate transporters play a pivotal role in maintaining non-toxin extracellular concentrations of glutamate in the brain. During anoxic conditions (such as occur during ischemia), the amount of extracellular glutamate in the brain rises dramatically. This is in part due to the fact that, under anoxic conditions, glutamate transporters work in reverse, thereby increasing rather than decreasing the amount of extracellular glutamate found in the brain. The resultingly high extracellular concentration of glutamate causes neuron death, with extremely deleterious consequences for motor and other brain functions, resulting in stroke, anoxia and other instances of organic brain dysfunction.

This important role for amino acid transporters in maintaining brain homeostasis of extracellular amino acid concentrations has provided the impetus for the search for and development of compounds to modulate and control transporter function. However, conventional screening methods require the use of animal brain slices in binding assays as a first step. This is suboptimal for a number of reasons, including interference in the binding assay by non-specific binding of heterologous (i.e., non-transporter) cell surface proteins expressed by brain cells in such slices; differential binding by cells other than neuronal cells present in the brain slice, such as glial cells or blood cells; and the possibility that putative drug binding behavior in animal brain cells will differ from the binding behavior in human brain cells in subtle but critical ways. The ability to synthesize human transporter molecules in vitro would provide an efficient and economical means for rational drug design and rapid screening of potentially useful compounds.

Amino acid transporters are known in the art, and some of these proteins have been isolated biochemically and their corresponding genes have been recently cloned using genetic engineering means.

Christensen el al., 1967, J. Biol. Chem. 242: 5237-5246 report the discovery of a neutral amino acid transporter (termed the ACS transporter) in Erlich ascites tumor cells.

Makowske & Christensen, 1982, J. Biol. Chem. 257: 14635-14638 provide a biochemical characterization of hepatic amino acid transport.

Kanner & Schuldiner, 1987, CRC Crit. Rev. Biochem. 22: 1-38 provide a review of the biochemistry of neurotransmitters.

Olney et al., 1990, Science 248: 596-599 disclose that the amino acid cysteine is a neurotoxin when present in excess extracellularly.

Wallace et al., 1990, J. Bacteriol. 172: 3214-3220 report the cloning and sequencing of a glutamate/aspartate transporter gene termed gltP from Escherichia coli strain K12.

Kim et al., 1991, Nature 352: 725-728 report the discovery that a cationic amino acid transporter is the cell surface target for infection by ecotropic retroviruses in mice.

Wang et al., 1991, Nature 352: 729-731 report the discovery that a cationic amino acid transporter is the cell surface target for infection by ecotropic retroviruses in mice.

Maenz et al., 1992, J. Biol. Chem. 267: 1510-1516 provide a biochemical characterization of amino acid transport in rabbit jejunal brush border membranes.

Bussolati et al., 1992, J. Biol. Chem. 267: 8330-8335 report that the ASC transporter acts in an electrochemically neutral manner so that sodium ion co-transport occurs without disrupting the normal membrane potential of the cells expressing the transporter.

Engelke et al., 1992, J. Bacteriol. 171: 5551-5560 report the cloning of a dicarboxylate carrier from Rhiwzobium meliloti.

Guastella et al., 1992, Proc. Nati. Acad. Sci. USA 89: 7189-7193 disclose the cloning of a sodium ion and chloride ion-dependent glycine transporter from a glioma cell line that is expressed in the rat forebrain and cerebellum.

Kavanaugh et al., 1992, J. Biol. Chem. 267: 22007-22009 report that biochemical characterization of a rat brain GABA transporter expressed in vitro in Xenopus laevis oocytes.

Storck et al., 1992, Proc. Nad. Acad. Sci. USA 89: 10955-10959 disclose the cloning and sequencing of a sodium ion-dependent glutamate/aspartate transporter from rat brain termed GLAST1.

Bouvier et al., ibid., disclose the biochemical characterization of a glial cell-derived glutamate transporter.

Pines et al., ibid., report the cloning and sequencing of a glial cell glutamate transporter from rat brain termed GLT-1.

Kanai & Hediger, 1992, Nature 360: 467-471 disclose the cloning and sequencing of a sodium ion-dependent, high affinity glutamate transporter from rabbit small intestine termed EAAC1.

Kong et al., 1993, J. Biol. Chem. 268: 1509-1512 report the cloning and sequencing of a sodium-ion dependent neutral amino acid transporter of the A type that is homologous to a sodium-ion dependent glucose transporter.

Nicholls & Attwell, ibid., review the role of amino acids and amino acid transporters in normal and pathological brain functions.

SUMMARY OF THE INVENTION

The present invention relates to the cloning, expression and functional characterization of mammalian amino acid transporter genes. The invention comprises nucleic acids, each nucleic acid having a nucleotide sequence of a novel amino acid transporter gene. The nucleic acids provided by the invention each comprise a complementary DNA (cDNA) copy of the corresponding mRNA transcribed in vivo from each of the amino acid transporter genes of the invention. Also provided are the deduced amino acid sequences of each the cognate proteins of the cDNAs provided by the invention.

This invention provides nucleic acids, nucleic acid hybridization probes, recombinant eukaryotic expression constructs capable of expressing the amino acid transporters of the invention in cultures of transformed cells, such cultures of transformed eukaryotic cells that synthesize the amino acid transporters of the invention, homogeneous compositions of each of the amino acid transporter proteins, and antibodies against and epitopes of each of the amino acid transporter proteins of the invention. Methods for characterizing these transporter proteins and methods for using these proteins in the development of agents having pharmacological uses related to these transporter proteins are also provided by the invention.

In a first aspect, the invention provides a nucleic acid having a nucleotide sequence encoding a human neutral amino acid transporter that is the ASCT1 transporter (SEQ ID No:2). In this embodiment of the invention, the nucleotide sequence includes 1680 nucleotides of the human ASCT1 cDNA comprising 1596 nucleotides of coding sequence, 30 nucleotides of 5′ untranslated sequence and 54 nucleotides of 3′ untranslated sequence. In this embodiment of the invention, the nucleotide sequence of the ASCT1 transporter consists essentially of the nucleotide sequence depicted in FIG. 1 (SEQ ID No:2). The use of the term “consisting essentially of” herein is meant to encompass the disclosed sequence and includes allelic variations of this nucleotide sequence, either naturally occurring or the product of in vitro chemical or genetic modification. Each such variant will be understood to have essentially the same nucleotide sequence as the nucleotide sequence of the corresponding ASCT1 disclosed herein.

The corresponding ASCT1 protein molecule, having the deduced amino acid sequence consisting essentially of the sequence shown in FIG. 1 (SEQ ID No.:3), is also claimed as an aspect of the invention. The use of the term “consisting essentially of” herein is as described above. Similarly, the corresponding ASCT1 protein molecule, having the deduced amino acid sequence consisting essentially of the sequence shown in FIG. 1 (SEQ ID No.:3), is also claimed as an aspect of the invention. ASCT1 protein molecules provided by the invention are understood to have substantially the same biological properties as the ASCT1 protein molecule encoded by the nucleotide sequence described herein.

In another aspect, the invention comprises a homogeneous composition of the 55.9 kD mammalian ASCT1 transporter or derivative thereof, said size being understood to be the size of the protein before any post-translational modifications thereof. The amino acid sequence of the ASCT1 transporter or derivative thereof preferably consists essentially of the amino acid sequence of the human ASCT1 transporter protein shown in FIG. 1 (SEQ ID No:3).

In a second aspect, the invention provides a nucleic acid having a nucleotide sequence encoding a human excitatory amino acid transporter that is the EAAT1 transporter (SEQ ID No:4). In this embodiment of the invention, the nucleotide sequence includes 1680 nucleotides of the human EAAT1 cDNA comprising 1626 nucleotides of coding sequence, 30 nucleotides of 5′ untranslated sequence and 24 nucleotides of 3′ untranslated sequence. In this embodiment of the invention, the nucleotide sequence of the EAAT1 transporter consists essentially of the nucleotide sequence depicted in FIG. 2 (SEQ ID No:4). The use of the term “consisting essentially of” herein is as described above.

In another aspect, the invention comprises a homogeneous composition of the 59.5 kilodalton (kD) mammalian EAAT1 transporter or derivative thereof, said size being understood to be the size of the protein before any post-translational modifications thereof. The amino acid sequence of the EAAT1 transporter or derivative thereof preferably consists essentially of the amino acid sequence of the human EAAT1 transporter protein shown in FIG. 2 (SEQ ID No:5). EAAT1 protein molecules provided by the invention are understood to have substantially the same biological properties as the EAAT1 protein molecule encoded by the nucleotide sequence described herein.

In a third aspect, the invention provides a nucleic acid having a nucleotide sequence encoding a human excitatory amino acid transporter that is the EAAT2 transporter (SEQ ID No:6). In this embodiment of the invention, the nucleotide sequence includes 1800 nucleotides of the human EAAT2 cDNA comprising 1722 nucleotides of coding sequence, 33 nucleotides of 5′ untranslated sequence and 45 nucleotides of 3′ untranslated sequence. In this embodiment of the invention, the nucleotide sequence of the EAAT2 transporter consists essentially of the nucleotide sequence depicted in FIG. 3 (SEQ ID No:6). The use of the term “consisting essentially of” herein is as described above.

The corresponding EAAT2 protein molecule, having the deduced amino acid sequence consisting essentially of the sequence shown in FIG. 3 (SEQ ID No.:7), is also claimed as an aspect of the invention. EAAT2 protein molecules provided by the invention are understood to have substantially the same biological properties as the EAAT2 protein molecule encoded by the nucleotide sequence described herein.

In another aspect, the invention comprises a homogeneous composition of the 62.1 kD mammalian EAAT2 transporter or derivative thereof, said size being understood to be the size of the protein before any post-translational modifications thereof. The amino acid sequence of the EAAT2 transporter or derivative thereof preferably consists essentially of the amino acid sequence of the human EAAT2 transporter protein shown in FIG. 3 (SEQ ID No:7).

In yet another aspect, the invention provides a nucleic acid having a nucleotide sequence encoding a human excitatory amino acid transporter that is the EAAT3 transporter (SEQ ID No:8). In this embodiment of the invention, the nucleotide sequence includes 1674 nucleotides of the human EAAT3 cDNA comprising 1575 nucleotides of coding sequence, 15 nucleotides of 5′ untranslated sequence and 84 nucleotides of 3′ untranslated sequence. In this embodiment of the invention, the nucleotide sequence of the EAAT3 transporter consists essentially of the nucleotide sequence depicted in FIG. 4 (SEQ ID No:8). The use of the term “consisting essentially of” herein is as described above.

The corresponding EAAT3 protein molecule, having the deduced amino acid sequence consisting essentially of the sequence shown in FIG. 4 (SEQ ID No.:9), is also claimed as an aspect of the invention. EAAT3 protein molecules provided by the invention are understood to have substantially the same biological properties as the EAAT3 protein molecule encoded by the nucleotide sequence described herein.

In another aspect, the invention comprises a homogeneous composition of the 57.2 kD mammalian EAAT3 transporter or derivative thereof, said size being understood to be the size of the protein before any post-translational modifications thereof. The amino acid sequence of the EAAT3 transporter or derivative thereof preferably consists essentially of the amino acid sequence of the human EAAT3 transporter protein shown in FIG. 4 (SEQ ID No:9).

This invention provides both nucleotide and amino acid probes derived from the sequences herein provided. The invention includes probes isolated from either cDNA or genomic DNA, as well as probes made synthetically with the sequence information derived therefrom. The invention specifically includes but is not limited to oligonucleotide, nick-translated, random primed, or in vitro amplified probes made using cDNA or genomic clone embodying the invention, and oligonucleotide and other synthetic probes synthesized chemically using the nucleotide sequence information of cDNA or genomic clone embodiments of the invention.

It is a further object of this invention to provide such nucleic acid hybridization probes to determine the pattern, amount and extent of expression of these transporter genes in various tissues of mammals, including humans. It is also an object of the present invention to provide nucleic acid hybridization probes derived from the sequences of the amino acid transporter genes of the invention to be used for the detection and diagnosis of genetic diseases. It is an object of this invention to provide nucleic acid hybridization probes derived from the DNA sequences of the amino acid transporter genes herein disclosed to be used for the detection of novel related receptor genes.

The present invention also includes synthetic peptides made using the nucleotide sequence information comprising the cDNA embodiments of the invention. The invention includes either naturally occurring or synthetic peptides which may be used as antigens for the production of amino acid transporter-specific antibodies, or used for competitors of amino acid transporter molecules for amino acid, agonist, antagonist or drug binding, or to be used for the production of inhibitors of the binding of agonists or antagonists or analogues thereof to such amino acid transporter molecules.

The present invention also provides antibodies against and epitopes of the mammalian amino acid transporter molecules of the invention. It is an object of the present invention to provide antibodies that are immunologically reactive to the amino acid transporters of the invention. It is a particular object to provide monoclonal antibodies against these amino acid transporters, must preferably the human excitatory and neutral amino acid transporters as herein disclosed. Hybridoma cell lines producing such antibodies are also objects of the invention. It is envisioned at such hybridoma cell lines may be produced as the result of fusion between a non-immunoglobulin producing mouse myeloma cell line and spleen cells derived from a mouse immunized with a cell line which expresses antigens or epitopes of an amino acid transporter of the invention. The present invention also provides hybridoma cell lines that produces such antibodies, and can be injected into a living mouse to provide an ascites fluid from the mouse that is comprised of such antibodies. It is a further object of the invention to provide immunologically-active epitopes of the amino acid transporters of the invention. Chimeric antibodies immunologically reactive against the amino acid transporter proteins of the invention are also within the scope of this invention.

The present invention provides recombinant expression constructs comprising a nucleic acid encoding an amino acid transporter of the invention wherein the construct is capable of expressing the encoded amino acid transporter in cultures of cells transformed with the construct. Preferred embodiments of such constructs comprise the human EAAT1 cDNA (SEQ ID No.:4), the human EAAT2 cDNA (SEQ ID No.:6), the human EAAT3 cDNA (SEQ ID No.:8), and human ASCT1 cDNA (SEQ ID No.:2), each construct being capable of expressing the amino acid transporter encoded therein in cells transformed with the construct.

The invention also provides cultures cells transformed with the recombinant expression constructs of the invention, each such cultures being capable of and in fact expressing the amino acid transporter encoded in the transforming construct.

The present invention also includes within its scope protein preparations of prokaryotic and eukaryotic cell membranes containing at least one of the amino acid transporter proteins of the invention, derived from cultures of prokaryotic or eukaryotic cells, respectively, transformed with the recombinant expression constructs of the invention. In a preferred embodiment, each preparation of such cell membranes comprises one species of the amino acid transporter proteins of the invention.

The invention also provides methods for screening compounds for their ability to inhibit, facilitate or modulate the biochemical activity of the amino acid transporter molecules of the invention, for use in the in vitro screening of novel agonist and antagonist compounds. In preferred embodiments, cells transformed with a recombinant expression construct of the invention are contacted with such a compound, and the effect of the compound on the transport of the appropriate amino acid is assayed. Additional preferred embodiments comprise quantitative analyses of such effects.

The present invention is also useful for the detection of analogues, agonists or antagonists, known or unknown, of the amino acid transporters of the invention, either naturally occurring or embodied as a drug. In preferred embodiments, such analogues, agonists or antagonists may be detected in blood, saliva, semen, cerebrospinal fluid, plasma, lymph, or any other bodily fluid.

Specific preferred embodiments of the present invention will become evident from the following more detailed description of certain preferred embodiments and the claims.

DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E illustrates the nucleotide (SEQ ID No.:2) and amino acid (SEQ ID No.:3) sequences of the human ASCT1 neutral amino acid transporter.

FIGS. 2A-2E illustrates the nucicotide (SEQ ID No.:4) and amino acid (SEQ ID No.:5) sequences of the human EAAT1 excitatory amino acid transporter.

FIGS. 3A-3F illustrates the nucleotide (SEQ ID No.:6) and amino acid (SEQ ID No.:7) sequences of the human EAAT2 excitatory amino acid transporter.

FIGS. 4A-4E illustrates the nucleotide (SEQ ID No.:8) and amino acid (SEQ ID No.:9) sequences of the human EAAT3 excitatory amino acid transporter.

FIGS. 5A & 5B presents an amino acid sequence comparison between human ASCT1, GLAST 1, GLT1 and EAAC1.

FIGS. 6A-6C illustrates transmembrane electrochemical currents in Xenopus laevis oocytes microinjected with RNA encoding ASCT1 and contacted with the indicated amino acids (FIG. 6A); the amino acid concentration dependence of such electrochemical currents (FIG. 6B); and a plot of normalized current vs. amino acid concentration illustrating the kinetic parameters of amino acid transport (FIG. 6C).

FIGS. 7A-7F presents glutamate transporter kinetics of EAAT1 (FIG. 7A & B), EAAT2 (FIG. 7C & D) and EAAT3 (FIG. 7E & 7F).

FIGS. 8A-8C represents the pharmacological responsiveness of glutamate transport by the human excitatory amino acid transporters EAAT1, EAAT2 and EAAT3 when contacted with the indicated competitors/inhibitors 1 μL-glutamate and inhibitor/competitor concentrations of 3 μM, 100 μM or 3 mM at the indicated concentrations.

FIG. 9 shows the pattern of expression of EAAT1, EAAT2, EAAT3 and ASCT1 in human tissues; β-actin is shown as a control for amount of RNA in each lane.

FIG. 10 shows the pattern of expression of EAAT1, EAAT2, EAAT3 and ASCT1 in human brain tissue; β-actin is shown as a control for the amount of RNA in each lane.

FIGS. 11A and 11B illustrates the degree of predicted amino acid sequence homology between the novel human glutamate transporters EAAT1, EAAT2 and EAAT3; overbars indicate nine regions of hydrophobicity determined using the algorithm of Eisenberg et al., and potential sites of N-linked glycosylation are shown by the circled asparagine (N) residues.

FIGS. 12A through 12C illustrate electrogenic uptake of various amino acids (FIG. 12A) and the concentration dependence of such uptake of L-glutamate (FIGS. 12B and 12C) in Xenopus laevis oocytes expressing the EAAT1 amino acid transporter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “human amino acid transporter EAAT1” as used herein refers to proteins consisting essentially of, and having substantially the same biological activity as, the protein encoded by the nucleic acid depicted in FIGS. 2A-2E (SEQ ID No.:4). This definition is intended to encompass natural allelic variations in the EAAT1 sequence. Cloned nucleic acid provided by the present invention may encode EAAT1 protein of any species of origin, including, for example, mouse, rat, rabbit, cat, and human, but preferably the nucleic acid provided by the invention encodes EAAT1 receptors of mammalian, most preferably human, origin.

The term “human amino acid transporter EAAT2” as used herein refers to proteins consisting essentially of, and having substantially the same biological activity as, the protein encoded by the nucleic acid depicted in FIGS. 3A-3F (SEQ ID No.:6). This definition is intended to encompass natural allelic variations in the EAAT2 sequence. Cloned nucleic acid provided by the present invention may encode EAAT2 protein of any species of origin, including, for example, mouse, rat, rabbit, cat, and human, but preferably the nucleic acid provided by the invention encodes EAAT2 receptors of mammalian, most preferably human, origin.

The term “human amino acid transporter EAAT3” as used herein refers to proteins consisting essentially of, and having substantially the same biological activity as, the protein encoded by the nucleic acid depicted in FIGS. 4A-4E (SEQ ID No.:8). This definition is intended to encompass natural allelic variations in the EAAT3 sequence. Cloned nucleic acid provided by the present invention may encode EAAT3 protein of any species of origin, including, for example, mouse, rat, rabbit, cat, and human, but preferably the nucleic acid provided by the invention encodes EAAT3 receptors of mammalian, most preferably human, origin.

The term “human amino acid transporter ASCT1” as used herein refers to proteins consisting essentially of, and having substantially the same biological activity as, the protein encoded by the nucleic acid depicted in FIGS. 1A-1E (SEQ ID No.:2). This definition is intended to encompass natural allelic variations in the ASCT1 sequence. Cloned nucleic acid provided by the present invention may encode ASCT1 protein of any species of origin, including, for example, mouse, rat, rabbit, cat, and human, but preferably the nucleic acid provided by the invention encodes ASCT1 receptors of mammalian, most preferably human, origin.

Each of the nucleic acid hybridization probes provided by the invention comprise DNA or RNA consisting essentially of the nucleotide sequence of one of the amino acid transporters, depicted in FIGS. 1A through 1E, FIGS. 2A through 2E, FIGS. 3A through 3F and FIGS. 4A through 4E (SEQ ID Nos.:2,4,6,8), or any portion thereof effective in nucleic acid hybridization. Mixtures of such nucleic acid hybridization probes are also within the scope of this embodiment of the invention. Nucleic acid probes as provided herein are useful for detecting amino acid transporter gene expression in cells and tissues using techniques well-known in the art, including but not limited to Northern blot hybridization, in situ hybridization and Southern hybridization to reverse transcriptase—polymerase chain reaction product DNAs. The A probes provided by the present invention, including oligonucleotides probes derived therefrom, are useful are also useful for Southern hybridization of mammalian, preferably human, genomic DNA for screening for restriction fragment length polymorphism (RFLP) associated with certain genetic disorders.

The production of proteins such as these amino acid transporter molecules from cloned genes by genetic engineering means is well known in this art. The discussion which follows is accordingly intended as an overview of this field, and is not intended to reflect the full state of the art.

DNA encoding an amino acid transporter may be obtained, in view of the instant disclosure, by chemical synthesis, by screening reverse transcripts of mRNA from appropriate cells or cell line cultures, by screening genomic libraries from appropriate cells, or by combinations of these procedures, as illustrated below. Screening of mRNA or genomic DNA may be carried out with oligonucleotide probes generated from the nucleic acid sequence information from each of the amino acid transporters disclosed herein. Probes may be labeled with a detectable group such as a fluorescent group, a radioactive atom or a chemiluminescent group in accordance with know procedures and used in conventional hybridization assays, as described in greater detail in the Examples below. In the alternative, amino acid transporter-derived nucleic acid sequences may be obtained by use of the polymerase chain reaction (PCR) procedure, using PCR oligonucleotide primers corresponding to nucleic acid sequence information derived from an amino acid transporter as provided herein. See U.S. Pat. Nos. 4,683,195 to Mullis et al. and 4,683,202 to Mullis.

Each of the amino acid transporter proteins may be synthesized in host cells transformed with a recombinant expression construct comprising a nucleic acid encoding the particular amino acid transporter cDNA. Such recombinant expression constructs can also be comprised of a vector that is a replicable DNA construct. Vectors are used herein either to amplify DNA encoding an amino acid transporter and/or to express DNA encoding an amino acid transporter gene. For the purposes of this invention, a recombinant expression construct is a replicable DNA construct in which a nucleic acid encoding an amino acid transporter is operably linked to suitable control sequences capable of effecting the expression of the amino acid transporter in a suitable host.

The need for such control sequences will vary depending upon the host selected and the transformation method chosen. Generally, control sequences include a transcriptional promoter, an optional operator sequence to control transcription, a sequence encoding suitable mRNA ribosomal binding sites, and sequences which control the termination of transcription and translation. Amplification vectors do not require expression control domains. All that is needed is the ability to replicate in a host, usually conferred by an origin of replication, and a selection gene to facilitate recognition of transformants. See, Sambrook et al., 1990, Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Press: New York).

Vectors useful for practicing the present invention include plasmids, viruses (including phage), retroviruses, and integratable DNA fragments (i.e., fragments integratable into the host genome by homologous recombination). The vector replicates and functions independently of the host genome, or may, in some instances, integrate into the genome itself. Suitable vectors will contain replicon and control sequences which are derived from species compatible with the intended expression host. A preferred vector is pCMV5 (Andersson et al., 1989, J. Biol. Chem. 264: 8222-8229). Transformed host cells are cells which have been transformed or transfected with recombinant expression constructs made using recombinant DNA techniques and comprising nucleic acid encoding an amino acid transporter protein. Preferred host cells are COS-7 cells (Gluzman, 1981, Cell 23: 175-182). Transformed host cells may express the amino acid transporter protein, but host cells transformed for purposes of cloning or amplifying nucleic acid hybridization probe DNA need not express the transporter. When expressed, each of the amino acid transporters of the invention will typically be located in the host cell membrane. See, Sambrook et al., ibid.

Cultures of cells derived from multicellular organisms are a desirable host for recombinant amino acid transporter protein synthesis. In principal, any higher eukaryotic cell culture is useful, whether from vertebrate or invertebrate culture. However, mammalian cells are preferred, as illustrated in the Examples. Propagation of such cells in cell culture has become a routine procedure. See Tissue Culture, Academic Press, Kruse & Patterson, editors (1973). Examples of useful host cell lines are human 293 cells, VERO and HeLa cells, Chinese hamster ovary (CHO) cell lines, and WI138, BHK, COS-7, CV, and MDCK cell lines. COS-7 cells are preferred.

The invention provides homogeneous compositions of each of the human EAAT1, EAAT2, EAAT3 and ASCT1 amino acid transporter proteins produced by transformed eukaryotic cells as provided herein. Each such homogeneous composition is intended to be comprised of the corresponding amino acid transporter protein that comprises at least 90% of the protein in such a homogenous composition. The invention also provides membrane preparation from cells expressing each of the amino acid transporter proteins as the result of transformation with a recombinant expression construct, as described herein.

Amino acid transporter proteins made from cloned genes in accordance with the present invention may be used for screening amino acid analogues, or agonist or antagonists of amino acid transport, or for determining the amount of such agonists or antagonists in a solution of interest (e.g., blood plasma or serum). For example, host cells may be transformed with a recombinant expression construct of the present invention, an amino acid transporter expressed in those host cells, and the cells or membranes thereof used to screen compounds for their effect on amino acid transport activity. By selection of host cells that do not ordinarily express a particular amino acid transporter, pure preparations of membranes containing the transporter can be obtained.

The recombinant expression constructs of the present invention are useful in molecular biology to transform cells which do not ordinarily express a particular amino acid transporter to thereafter express this receptor. Such cells are useful as intermediates for making cell membrane preparations useful for transporter activity assays, which are in turn useful for drug screening. The recombinant expression constructs of the present invention may also be useful in gene therapy. Cloned genes of the present invention, or fragments thereof, may also be used in gene therapy carried out homologous recombination or site-directed mutagenesis. See generally Thomas & Capecchi, 1987, Cell 51: 503-512; Bertling, 1987, Bioscience Reports 7: 107-112; Smithies et al., 1985, Nature 317: 230-234.

Oligonucleotides of the present invention are useful as diagnostic tools for probing amino acid transporter gene expression in tissues of humans and other animals. For example, tissues are probed in situ with oligonucleotide probes carrying detectable groups by conventional autoradiographic techniques, to investigate native expression of this receptor or pathological conditions relating thereto. Further, chromosomes can be probed to investigate the presence or absence of the corresponding amino acid transporter gene, and potential pathological conditions related thereto.

The invention also provides antibodies that are immunologically reactive to the amino acid transporter proteins or epitopes thereof provided by the invention. The antibodies provided by the invention may be raised, using methods well known in the art, in animals by inoculation with cells that express an amino acid transporter or epitopes thereof, cell membranes from such cells, whether crude membrane preparations or membranes purified using methods well known in the art, or purified preparations of proteins, including fusion proteins, particularly fusion proteins comprising epitopes of the amino acid transporter proteins of the invention fused to heterologous proteins and expressed using genetic engineering means in bacterial, yeast or eukaryotic cells, said proteins being isolated from such cells to varying degrees of homogeneity using conventional biochemical means. Synthetic peptides made using established synthetic means in vitro and optionally conjugated with heterologous sequences of amino acids, are also encompassed in these methods to produce the antibodies of the invention. Animals that are used for such inoculations include individuals from species comprising cows, sheep, pigs, mice, rats, rabbits, hamsters, goats and primates. Preferred animals for inoculation are rodents (including mice, rats, hamsters) and rabbits. The most preferred animal is the mouse.

Cells that can be used for such inoculations, or for any of the other means used in the invention, include any cell line which naturally expresses one of the amino acid transporters provided by the invention, or any cell or cell line that expresses one of the amino acid transporters of the invention, or any epitope thereof, as a result of molecular or genetic engineering, or that has been treated to increase the expression of an endogenous or heterologous amino acid transporter protein by physical, biochemical or genetic means. Preferred cells are E. coli and insect SF9 cells, most preferably E. coli cells, that have been transformed with a recombinant expression construct of the invention encoding an amino acid transporter protein, and that express the transporter therefrom.

The present invention also provides monoclonal antibodies that are immunologically reactive with an epitope derived from an amino acid transporter of the invention, or fragment thereof, present on the surface of such cells, preferably E. coli cells. Such antibodies are made using methods and techniques well known to those of skill in the art. Monoclonal antibodies provided by the present invention are produced by hybridoma cell lines, that are also provided by the invention and that are made by methods well known in the art.

Hybridoma cell lines are made by fusing individual cells of a myeloma cell line with spleen cells derived from animals immunized with cells expressing an amino acid transporter of the invention, as described above. The myeloma cell lines used in the invention include lines derived from myelomas of mice, rats, hamsters, primates and humans. Preferred myeloma cell lines are from mouse, and the most preferred mouse myeloma cell line is P3X63-Ag8.653. The animals from whom spleens are obtained after immunization are rats, mice and hamsters, preferably mice, most preferably Balbic mice. Spleen cells and myeloma cells are fused using a number of methods well known in the art, including but not limited to incubation with inactivated Sendai virus and incubation in the presence of polyethylene glycol (PEG). The most preferred method for cell fusion is incubation in the presence of a solution of 45% (w/v) PEG-1450. Monoclonal antibodies produced by hybridoma cell lines can be harvested from cell culture supernatant fluids from in vitro cell growth; alternatively, hybridoma cells can be injected subcutaneously and/or into the peritoneal cavity of an animal, most preferably a mouse, and the monoclonal antibodies obtained from blood and/or ascites fluid.

Monoclonal antibodies provided by the present invention are also produced by recombinant genetic methods well known to those of skill in the art, and the present invention encompasses antibodies made by such methods that are immunologically reactive with an epitope of an amino acid transporter of the invention. The present invention also encompasses fragments, including but not limited to F(ab) and F(ab)₂ fragments, of such antibody. Fragments are produced by any number of methods, including but not limited to proteolytic cleavage, chemical synthesis or preparation of such fragments by means of genetic engineering technology. The present invention also encompasses single-chain antibodies that are immunologically reactive with an epitope of an amino acid transporter, made by methods known to those of skill in the art.

The present invention also encompasses an epitope of an amino acid transporter of the invention, comprised of sequences and/or a conformation of sequences present in the transporter molecule. This epitope may be naturally occurring, or may be the result of proteolytic cleavage of a transporter molecule and isolation of an epitope-containing peptide or may be obtained by synthesis of an epitope-containing peptide using methods well known to those skilled in the art. The present invention also encompasses epitope peptides produced as a result of genetic engineering technology and synthesized by genetically engineered prokaryotic or eukaryotic cells.

The invention also includes chimeric antibodies, comprised of light chain and heavy chain peptides immunologically reactive to an amino acid transporter-derived epitope. The chimeric antibodies embodied in the present invention include those that are derived from naturally occurring antibodies as well as chimeric antibodies made by means of genetic engineering technology well known to those of skill in the art.

The Examples which follow are illustrative of specific embodiments of the invention, and various uses thereof. They set forth for explanatory purposes only, and are not to be taken as limiting the invention.

EXAMPLE 1 Isolation of a Human Neutral Amino Acid Transporter cDNA

In order to clone a novel human neutral amino acid transporter, a cDNA library was prepared from human motor cortex mRNA using standard techniques [see Sambrook et al., 1990, Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Press: New York)]. Briefly, total RNA was isolated using the method of Chomczynski & Sacchi (1987, Anal. Biochem. 162: 156-159), wherein the tissue is disrupted and solubilized in a solution containing guanidinium isothiocyanate and the RNA purified by phenol/chloroform extractions. Total cellular RNA thus isolated was then enriched for poly (A⁺) mRNA by oligo (dT) chromatography. A mixture of oligo (dT)-primed and random-primed mRNA was converted to cDNA using the Superscript Choice System (Bethesda Research Labs, Gaithersburg, Md.). cDNA was ligated into the cloning vector λZAPII (Strategene, La Jolla, Calif.), packaged into phage heads using commercially-available packaging extracts (Strategene) and used to infect E. coli. Lawns of infected bacterial cells were used to make plaque lifts for hybridization using standard conditions (see Sambrook, et al., ibid.).

This cDNA library was hybridized with a ³²P-labeled oligonucleotide having the following sequence:

5′-CTG(A/G)GC(A/G)ATGAA(A/G)ATGGCA (SEQ ID NO:1). GCCAGGGC(C/T)TCATACAGGGCTGTGCC(A/G) TCCATGTT(A/G)ATGGT(A/G)GC-3′

(This oligonucleotide was obtained commercially from Oligos, Etc., Wilsonville, Oreg.). This oligonucleotide was chosen on the basis of shared homology between a cloned rat glutamate transporter gene (GLAST1) and the bacterial glutamate transporter gene gltP (see Storck et al, ibid. and Wallace et al., ibid.), which suggested an important and conserved structural motif. Hybridization was performed at 50° C. in a solution containing 0.5M Na₂HPO₄ (pH 7.15)/7% sodium dodecyl sulfate (SDS) and the filters were washed at 60° C. in 2× SSPE [0.36M NaCl/20 mM sodium phosphate (pH 7.7)/2 mM ethylenediamine tetraacetic acid (EDTA)] and 1% SDS. Hybridizing clones were identified by autoradiography at −70° C. using tungsten-containing intensifying screens (DuPont-NEN, Wilmington, Del.).

More than 20 positively-hybridizing clones were detected in screening experiments using the above-described primer. One of these clones was excised from the cloning vector in vivo by superinfection with a defective filamentous phage that recognizes and excises cloned insert sequences along with adjacent modified phage replication-form sequences (termed pBluescript SK and available from Strategene). This clone contained a 2.7 kilobase (kb) insert, which was sequenced using the dideoxy-chain termination method of Sanger et al. (1977, Proc. Natl. Acad. Sci. USA 74: 5463), using Sequenase 2.0, a modified form of bacteriophage T7 DNA polymerase (U.S. Biochemical Corp., Cleveland, Ohio). The nucleotide sequence of the portion of this clone containing an open reading frame (encoding the ASCT1 gene) is shown in FIGS. 1A-1E.

This ASCT1 clone (SEQ ID No.:2) was found to be comprised of about 180 bp of 5′ untranslated region, about 900 bp of 3′ untranslated region and an open reading frame of 1596 bp encoding the ASCT1 transporter protein (comprising 532 amino acids). The initiator methionine codon was found to be the first methionine codon 3′ to an in-frame stop codon and embedded within the consensus sequence for eukaryotic translation initiation (see Kozak, 1987, Nucleic Acids Res 15: 8125-8132). The ASCT1 amino acid sequence (SEQ ID No.:3; also shown in FIGS. 1A-1E) was found to exhibit similarity to other known glutamate transporter subtypes (an amino acid sequence comparison is shown in FIGS. 5A & 5B). An amino acid comparison between glutamate transporters from rat (GLAST1 and GLT-1) and rabbit (EAAC1) showed 39%, 34% and 39% sequence identity (respectively) between these amino acid transporter proteins (shown in FIGS. 5A & 5B by shaded boxes). This degree of sequence identity is comparable to the sequence identity between these glutamate subtypes themselves. Both the amino and carboxyl termini were found to be divergent between these transporter proteins, and diversity was also found in the extracellular domains of these putative protein sequences, which contain conserved potential N-glycosylation sites (shown in FIGS. 5A & 5B by open boxes). It was noted that a highly conserved sequence (comprising the amino acids —LYEA—) in the glutamate transporters was replaced by the unrelated amino acid sequence —IFQC— in the ASCT1 sequence (at positions 385-387 of the ASCT1 amino acid sequence shown in FIGS. 5A & 5B). 6-10 putative transmembrane domains were found using the algorithm of Eisenberg et al. (1984, J. Molec. Biol. 179: 125-142). On the basis of these data ASCT1 was determined to encode a related but distinct and novel member of the amino acid transporter family.

EXAMPLE 2 Isolation of Human Excitatory Amino Acid Transporter cDNA

The remaining (>20) positively-hybridizing clones from the human motor cortex cDNA library detected by hybridization with the primer described in Example 1 (SEQ ID No.:1) were isolated and the corresponding plamids obtained by in vivo excision after superinfection with defective phage as described in Example 1 above. These resulting plasmids were isolated and purified using conventional techniques (see Sambrook et al., ibid.). Four classes of clones were distinguished based on differential hybridization experiments using each clone as a hybridization probe against a panel of the remaining clones one after another, where conditions of hybridization stringency were varied to distinguish between each of the classes.

Representative clones from each class were sequenced as described in Example 1. One class of clones represented the ASCT1 cDNA sequences described in Example 1. The other three classes were found to encode novel proteins having amino acid sequences homologous to but distinct from the human ASCT1 sequence. Clone GT5 was determined to contain a 4.0 kb insert encoding a protein having a predicted amino acid sequence (termed EAAT1; SEQ ID No.:4) homologous to but distinct from the rat GLAST1 cDNA clone of Storck et al. (ibid.). Clone GT13 was determined to contain a 2.5 kb insert comprising an open reading frame corresponding to a full-length coding sequence for a novel human transporter gene termed EAAT2 (SEQ ID No.:6). Clone GT11 was found to contain a partial sequence of another novel human transporter termed EAAT3. The EAAT3 clone was used to re-screen the cDNA library described in Example 1. The result of these re-screening experiments was the isolation of Clone GT11B containing a full-length open reading frame encoding EAAT3 (SEQ ID No.:8).

FIGS. 11A & 11B shows the results of alignment of the predicted amino acid sequences of the three novel glutamate transporters of the invention. Nine regions of Eisenberg algorithm predicted hydrophobicity are denoted by overlining, and potential sites of N-linked glycosylation (consensus sequence N-X-S/T, where X is any amino acid) are indicated by the circles asparagine (N) residues. EAAT1 shares 47% (253/542) amino acid sequence identity with EAAT2 and 46% (262/574) sequence identity with EAAT3, whereas the EAAT2 sequence is 45% (259/574) identical to the predicted EAAT3 sequence. Cross-species comparisons of the predicted amino acid sequences of these novel human glutamate transporters revealed the following relationships: EAAT1 was found to be 96% homologous with the rat GLAST1 sequence (Storck et al., ibid.); EAAT2 was found to be 90% homologous with the rat GLT1 sequence (Pines et al., 1992, ibid.); and EAAT3 was found to be 93% homologous with the rabbit EAAC1 sequence (Kanai & Hediger, 1992, ibid.). These results indicate that EAAT1, EAAT2 and EAAT3 are related but distinct members of the glutamate transporter family of amino acid transporters.

EXAMPLE 3 Functional Expression of the ASCT1 Amino Acid Transporter Gene in Xenogus Oocytes

The sequence similarity between ASCT1 and the glutamate transporters GLAST1, EAAC1 and GLT-1 suggested that the protein encoded by ASCT1 was an amino acid transporter. The ability of the ASCT1 gene product to transport amino acids, and the identity of which amino acids might be transported by this gene product, was assayed in Xenopus laevis oocytes following microinjection of in vitro synthesized ASCT1 RNA.

Briefly, the coding sequence of the ASCT1 cDNA was isolated with unique flanking restriction sites using a PCR-based assay. In this assay, each of the complementary primers used for PCR amplification of the coding sequence contained a sequence encoding a unique restriction enzyme recognition site at the 5′ terminus of each PCR primer. For ASCT1, the sense primer contained a KpnI recognition sequence (GGTAC↓C), and the antisense primer contained an XbaI recognition sequence (T↓CTAGA) at their respective 5′ termini. Each of the PCR primers used for amplifying ASCT1 sequences had the following sequence:

ASCT1 sense primer: 5′-CGCGGGTACCGCCATGGAGAAGAGCAAC-3′ (SEQ ID NO:10); ASCT1 antisense primer: 5′-CGCGTCTAGATCACAGAACCGACTCCTTG-3′ (SEQ ID NO:11).

PCR amplification was performed for 30 cycles, each cycle comprising 1 minute at 94° C., 30 seconds at 55° C. and 2 minutes at 72° C. Following the PCR, the product of the amplification reaction was purified using standard techniques (Saiki et al., 1988, Science 239: 487-491). The DNA then digested with the restriction enzymes KpnI and XbaI and then cloned into the polylinker of an oocyte transcription vector (POTV; see Wang el al., 1991, Nature 352: 729-731) that had been digested with KpnI and XbaI. Synthetic RNA was then transcribed in vitro from this clone using the method of Kavanaugh et al. (1992, J. Biol. Chem. 267: 22007-22009) employing bacteriophage T7 RNA polymerase (New England Biolabs, Beverly, Mass.). 20-50 nL of ASCT1 RNA (at a concentration of about 400 μg/mL) was injected into defolliculated stage V-VI Xenopus oocytes excised from female Xenopus laevis anesthetized by immersion in 3-aminobenzoic acid for 60 min. Excised oocytes were treated with collagenase II (Sigma Chemical Co., St. Louis, Mo.) in calcium-free Barth's saline solution [comprising 88 mM NaCl, 1 mM KCl, 2.4 mM NaHCO₃, 0.82 mM MgSO₄, 7.5 mM Tris-HCl (pH 7.6), 50 U/mL Nystatin (Sigma) and 0.1 mg/mL gentamycin (Sigma)] for 60 min., and then incubated overnight at 15° C. in 50% Leibowitz's L-15 media (Grand Island Biological Co. (GIBCO), Long Island, N.Y.). After overnight incubation the oocytes were mechanically defolliculated and then were injected with ASCT-1 RNA and incubated at 19° C. for 48 h (see Kim el al., 1991, Nature 352: 725-728 for further details of Xenopus oocyte preparation and microinjection).

Amino acid transport in such oocytes was assayed using [³H] alanine, [³H] serine or [³⁵S] cysteine (obtained from New England Nuclear, Boston, Mass.). Briefly, microinjected oocytes were patch-lamped at −60 mV using a Dagan TEV-200 clamp amplifier with an Axon Instruments (Foster City, Calif.) TL-1 A/D interface controlled by pCLAMP software (Axon Instruments) (see Kavanaugh et al., 1992, J. Biol. Chem. 267: 22007-22009 for a detailed review of this methodology) and continuously superfused with ND-96 buffer (consisting of 96 mM NaCl/2 mM KCl/1.8 mM CaCl₂/1 mM MgCl₂/5 mM HEPES, pH 7.5). For transport measurements, this solution was changed to a solution containing varying concentrations of the radiolabeled amino acids in ND-96 buffer.

Three types of experiments were performed, the results of each being shown in FIGS. 6A-6C. As shown in FIG. 6A, when such oocytes were contacted with ND-96 buffer containing L-alanine, L-serine or L-cysteine, a hyperpolarization of the cell plasma membrane was produced as the result of inward currents of Na⁺ ion, as has been associated with other known amino acid transporters (see Nicholls, ibid.). In contrast, the amino acids L-lysine, L-glutamine, proline, glycine, methionine, arginine, glutamine, asparagine, and leucine, and the amino acid analogues N-methylalanine, had no effect at much higher concentrations (i.e., about 1 mM). Another amino acid analogue, 2-methylaminoisobutyric acid (MAIB), which is known to be specific for the amino acid transporter type A (Christensen et al., 1967, J. Biol. Chem. 242: 5237-5246), also had no effect at concentrations of 1 mM. Further, in competition experiments, contacting such oocytes with a solution containing MAIB at a concentration of 10 mM had no effect on the rate of uptake of [³H] alanine present at 100 μM. The response of the oocytes was also stercospecific (D-alanine was found to produce only 12±3% of the response produced by treatment of these oocytes with L-alanine) and Na⁺ ion-specific (no response was detected when Na⁺ ions were replaced by tris-hydroxyethylaminomethane buffer, shown in FIG. 6A). The rate of radiolabeled amino acid uptake (in pmol/min per oocyte, determined at an amino acid concentration of 100 μM) for the amino acids alanine, cysteine and serine are shown in Table I.

The uptake currents measured in ASCT1-injected oocytes were found to be both dose-dependent and saturable. FIG. 6B illustrates the dose-dependency of the electrochemical response of ASCT1-injected oocytes to L-alanine. The intensity of the response (equivalent to the amount of current flow into the cell) increased with the concentration of L-alanine from 10 μM to 1 mM. The saturability of this response is shown in FIG. 6C. In this Figure, the current, normalized to the maximum response obtained with L-alanine, is shown plotted against the extracellular amino acid concentration of each amino acid tested. For the L-stereoisomers of alanine, serine, cysteine and threonine, the inward current flux was found to saturate and reach a plateau at concentrations from 400-1000 μM. More detailed analyses of ithe kinetics of amino acid influx were performed by least squares linear regression analysis of induced inward current ([I]) plotted as a function of substrate amino acid concentration ([S]), using the equation shown in the legend of Table II. Data were averaged from all oocytes tested, and the results expressed as the mean±standard error are shown in Table 11.

These results indicated that the cloned ASCT1 cDNA derived from human motor cortex mRNA encoded an amino acid transporter that was specific for Alanine, Serine, Cysteine (and Threonine) and that amino acid transport activity was accompanied by an inward current flow mediated by sodium ions. These results demonstrated that the novel amino acid transporter isolated herein was related to but distinct from other, known transporters, such as the so-called ASC amino acid transporters (Christensen ei al., ibid.).

EXAMPLE 4 Functional Expression of the Glutamate Amino Acid Transporter Genes in Xenogus Oocytes

Similar series of experiments were performed using RNA synthesized in vitro from constructs containing each of the cloned glutamine transporter genes of the invention. In these experiments, each of the PCR primers used to amplify each of the glutamate transporter genes had the following sequence:

EAAT1 sense primer: 5′-CGCGGGTACCAATATGACTAAAAGCAATG-3′ (SEQ ID NO: 12); EAAT1 antisense primer: 5′-CGCGTCTAGACTACATCTTGGTTTCACTG-3′ (SEQ ID NO: 13); EAAT2 sense primer: 5′-CGCGGGTACCACCATGGCATCTACGGAAG-3′ (SEQ ID NO: 14); EAAT2 antisense-primer: 5′-CGCGTCTAGATTATTTCTCACGTTTCCAAG-3′ (SEQ ID NO: 15); EAAT3 sense primer: 5′-CGCGGGTACCGCCATGGGGAAACCGGCG-3′ (SEQ ID NO: 16); EAAT3 antisense primer: 5′-CGCGGGATCCCTAGAACTGTGAGGTCTG-3′ (SEQ ID NO: 17).

As can be determined by inspection of these sequences, each of the sense primers contained a KpnI recognition sequence (GGTAC↓C), and each of the antisense primers contained an XbaI recognition sequence (T↓CTAGA) at the 5′ terminus of each primer for EAAT1 and EAAT2. For EAAT3, the sense primer contained a KpnI recognition sequence, and the antisense primer contained a BamHI recognition sequence (G↓GATCC) at the 5′ terminus of each primer.

PCR amplification was performed for 30 cycles, each cycle comprising 1 minute at 94° C., 30 seconds at 50° C. and 2 minutes at 72° C. Following the PCR, each of the PCR products was isolated and cloned into pOTV as described in Example 3, from which RNA encoding each glutamate transporter was synthesized in vitro as described.

Such RNA preparations were each introduced into Xenopus oocytes as descnbed in Example 3 to enable expression therein. Amino acid uptake experiments were performed on such oocytes expressing each of the glutamate transporters, also as described in Example 3. Results of such experiments are shown in FIGS. 12A through 12C. FIG. 12A shows electrogenic uptake of various amino acids in EAAT1-expressing oocytes. Both L-glutamate and L-aspartate caused inward currents as high as several microamps when added to the incubation media (ND-96) at a concentration of 100 μM. In contrast, incubation of EAAT1-expressing oocytes with L-alanine and L-serine at ten-fold higher concentrations (i.e., 1000 μM) did not result in electrogenic uptake of these amino acids. Uptake was found to be stereospecific, since L-glutamate incubation did not result in the generation of an inward electric current, and sodium-ion specific, since electrogenic uptake of L-glutamate was abolished by incubation in sodium ion-free media (choline was used to replace sodium in these incubations).

These experiments also demonstrated the surprising result that cysteine, when present at high enough extracellular concentrations (i.e., 1000 μM) was capable of being electrogenically transported by the EAAT1 transporter. Cysteine had not previously been reported to be a glutamate transporter substrate; however, amino acid sequence analysis of the EAAT1 transporter showed structural similarities between EAAT1 and the ASCT1 transporter, which was demonstrated herein to transport cysteine (see Example 3). As will be discussed in detail below, the EAAT1 transporter displays a K_(m) for glutamate of 54 μM; in contrast, the K_(m) for cysteine was found to be 300 μM. The EAAT1 transporter thus displays a pattern of substrate specificity that is distinct from that of any known glutamate transporter.

FIGS. 12B and 12C illustrate the results of biochemical analysis of substrate affinity of the EAAT1 transporter for glutamate, said results being plotted as current versus substrate concentration to yield an estimate of the K_(m). These experiments were performed essentially as described for the ASCT1 transporter in Example 3. Patch-lamped oocytes expressing the EAAT1 transporter were incubated with varying extracellular concentrations of L-glutamate, and the magnitude of the resulting inward currents determined. From these experiments, the plotted relationship between the magnitude of the inward current and the extracellular L-glutamate concentration was determined, resulting in an estimate for K_(m) equal to 54 μM for L-glutamate. These results were in good agreement with results obtained in COS-7 cells expressing the EAAT1 transporter, described hereinbelow (see Example 5).

EXAMPLE 5 Functional Expression of the Amino Acid Transporter Genes in COS-7 Cells

DNA fragments comprising the coding sequences of the novel glutamate transporter genes of the invention were excised from the POTV constructs described in Example 3 and subcloned into the mammalian expression plasmid pCMV5 (Anderson et al., 1989, J. Biol. Chem. 264: 8222-8229). These mammalian expression constructs were used for transient expression assays of glutamate transporter protein function after transfection of each of these constructs into COS-7 cells (Gluzman, 1981, Cell 23: 175-182).

Each of the pCMV5 constructs corresponding to EAAT1, EAAT2 and EAAT3 were introduced into COS-7 cells by DEAE-dextran facilitated transfection (see Sambrook et al., ibid.). Two day following transfection, the transfected cells were washed three times in phosphate-buffered saline (PBS) and then incubated with a mixture of radiolabeled amino acid ([³H]-L-glutamate or [³H]-D-aspartate; Dupont-NEN) and non-radiolabeled amino acid for 10 min. After incubation, the cells were washed three times with ice-cold PBS, solubilized with a solution of 0.1% sodium dodecyl sulfate (SDS) and the amount of radioactivity associated with the cells determined using standard liquid scintillation counting methods. The results of these experiments showed that cells transfected with each of the glutamate transporter constructs accumulated significantly-higher (between 10- and 100-fold higher) amounts of radioactivity than did mock (i.e., pCMV5 plasmid) transfected COS-7 cells (which accumulation represented endogenous COS-7 cell uptake of radioactive glutamate). The course of radioactive glutamate uptake was found to be linear for at least 20 min in assays performed at room temperature.

These results are shown in FIGS. 7A-7F. In the Figure, EAAT1 transporter kinetics of glutamate uptake are depicted in FIG. 7A and of aspartate are shown in FIG. 7B. Similarly, EAAT2 kinetics for glutamate and aspartate are shown in FIGS. 7C & 7D, respectively. Finally, EAAT3 kinetics are shown in FIG. 7E (glutamate) and FIG. 7F (aspartate). Each data point was determined by incubating a COS cell culture transfected with the appropriate pCMV5-glutamate transporter clone with 100 nM of radiolabeled amino acid and increasing amounts of unlabeled amino acid. Results are plotted as uptake velocity (in pmol/cell culture/min) minus endogenous uptake versus total amino acid concentration, and each data point was performed in triplicate. The results show that both glutamate and aspartate uptake mediated by each of the three novel human glutamate transporters is saturable. Insets in each Panel depict Eadie-Hofstee plots of initial velocity data, from which K_(m) values were determined. The K_(m) values are shown as the mean±standard error based on at least three independent experiments. These results show that each of the three novel transporter proteins comprising the instant invention is functionally competent as an amino acid transporter when expresed in a culture of mammalian cells, and that each of the novel transporters encoded by the cDNA clones EAAT1, EAAT2 and EAAT3 displays a collection of biochemical properties consistent with their designation as human glutamate transporter proteins.

EXAMPLE 6 Inhibitor Potency Analyses Using COS-7 Cells Expressing Amino Acid Transporter Proteins

COS-7 cell cultures transformed with pCMVS-human glutamate transporter constructs as described in Example 4 were used to characterize the pharmacological properties of each of these transporter proteins relative to a variety of known glutamate transporter inhibitors. These assays were performed essentially as described in Example 4, with the exception that varying amounts of each of a number of known inhibitor compounds were included in the incubations.

The results of these experiments are shown in FIGS. 8A-8C. The data in FIGS. 8A-8C represent the pharmacological responsiveness of glutamate transport by the human excitatory amino acid transporters EAAT1, EAAT2 and EAAT3 when contacted with the following competitors/inhibitors: L-threo-β-hydroxyaspartate (THA); L-trans-pyrrolidine-2,4-dicarboxylate (PDC); L-serine-O-sulfate (SOS); dihydrokainate (DHK); and kainate (KAI). In these experiments, uptake of 1 μM of [³]-L-glutamate was determined in the presence of the indicated amounts of each of the inhibitors. As can be seen from the Figures, each of the glutamate transporter proteins of the invention displays a characteristic pattern of sensitivity to the inhibitors. Thus, the relative potency of inhibition of radiolabeled glutamate uptake was found to be as follows for the EAAT1 and EAAT3 transporter proteins:

THA<PDC<SOS<<DHK, KAI,

whereas the inhibition pattern for EAAT2 was as follows:

PDC<TRA<DHK<KAI<SOS.

These results, as well as results obtained from similar experiments performed with L-cysteate, L-cysteine sulfinic acid, β-glutamate and L-aspartate-β-hydroxymate, are shown in Table III. Even though the relative pattern of inhibition was the same for EAAT1 and EAAT3, the results shown in the Table support the fining that each of the glutamate transporters of the invention is uniquely characterized by its sensitivity to this panel of glutamate uptake inhibitors.

In addition, a number of reported inhibitors were found to be ineffective when tested with COS cell culture expressing each of the novel glutamate transporter proteins of the invention. These include cis-1-aminocyclobutane-1,3-dicarboxylate, L-pyroglutamicacid, S-sulfo-L-cysteine, N-acetyl aspartylglutamate, N-methyl-D-aspartate (NMDA) and quisqualate. α-aminoadipate, a classical inhibitor of glutamate uptake, exhibited only low potency when tested against all three EAAT subtypes. These results of functional assays support the conclusion arrived at from structural analysis (i.e., nucleic acid and amino acid sequence analyses) that the glutamate transporter cDNAs and proteins of the invention are novel mammalian transporter species.

EXAMPLE 7 Tissue Distribution of Amino Acid Transporter Expression

The tissue distribution of mRNA corresponding to expression of the amino acid transporters disclosed herein was determined in various tissues by Northern hybridization experiments (see Sambrook et al., ibid.). The results of these experiments are shown in FIGS. 9 and 10.

A panel of tissue samples was examined by Northern hybridization analysis performed under high stringency conditions as follows. A nylon filter containing 2 μg human peripheral tissue poly(A)⁺ RNA was obtained from Clonetech Laboratories (Palo Alto, Calif.), and a similar filter was prepared containing human brain region RNA as follows. Total RNA was isolated from human brain region tissue obtained from the Oregon Brain Repository and 20 μg/region were size-fractionated by denaturing formaldehyde agarose gel electrophoresis (see Sambrook et al., ibid.). Fractionated RNA was then transferred to a nylon filter using the Northern blot/capillary-osmotic technique. Northern hybridization of both filters was performed individually with ³²P-labeled amino acid transporter-specific probes for each transporter to be analyzed. Probes were derived from amino acid transporter coding sequences and labeled using ³²P-labeled dCTP by the random primer method (Boehringer-Mannheim, Indianapolis Ind.). Filters were hybridized overnight at 42° C. individually with each radiolabeled probe (at a concentration of 10⁶ cpm/mL) in a solution of 5× SSPE/50% formamide/7.5× Denhardt's solution (comprising 0.15 g/100 mL each of Ficoll, polyvinylpyrrolidone and bovine serum albumin)/2% SDS and 100 μg/mL denatured salmon-sperm DNA. Following hybridization, filters were washed twice for 30 min at room temperature in 2× SSPE/0.1% SDS and twice for 20 min at 50° C. in 0.1× SSPE/0.1 % SDS. Hybridizing RNAs were visualized by autoradiography at −70° C. using intensifying screens. The filters were subsequently re-probed as described with a radiolabeled human β-actin probe (Clonetech) as a positive control.

The results of these experiments are shown in FIGS. 9 and 10. FIG. 9 illustrates expression of each of the amino acid transporters in human heart, brain, placenta, lung, liver, muscle, kidney and pancreas. The size (in kb) of the transcripts corresponding to expression of each transporter are displayed along the right-hand border of each panel. As is seen from these autoradiographs, EAAT1 is expressed predominantly in brain, heart and muscle, to a lesser extent in placenta and lung, weakly in liver, and at levels below the ability of this assay to detect in kidney and the pancreas (if at all). EAAT2 is expressed in brain, and to a lesser extent in placenta; expression was not detected in any other tissue tested. EAAT3 is expressed predominantly in the kidney, but significant expression was also detected in brain, placenta, and lung. ASCT1 is expressed in all tissues tested as at least one of three differently-sized transcripts, possibly corresponding to differential RNA processing during expression of this transporter (which result might be due in the alternative to the utilization of alternative polyadenylation sites found in the 3′ untranslated region). These results demonstrate that the amino acid transporters disclosed herein are encoded by separate and distinct, albeit related, genes and that each transporter has a unique pattern of tissue-specific expression.

FIG. 10 shows the distribution of these amino acid transporter transcripts in different human brain regions. Varying expression levels were found for each of the amino acid transporters in all brain regions examined. These results support the conclusion that the amino acid transporters of the invention may play an important role in normal brain function, and that disruption of amino acid transport by these transporter may be important determinants in organic brain dysfunction, as a result of ischemia or anoxia.

EXAMPLE 8 Construction of Vaccinia Virus-Recombinant Expression Constructs for Functional Expression of Amino Acid Transporters

Using an alternative approach, the amino acid transporter proteins of the invention are expressed in human HeLa (vulval adenocarcinoma) cells via a vaccinia virus-based construct. In these experiments, each of the amino acid transporter cDNAs of the invention are excised from their respective pOTV-containing constructs and subcloned into a modified pBluescript (Strategene) vector wherein each of the amino acid transporter cDNAs described above is under the control of a bacteriophage T7 RNA polymerase promoter (as is described in Blakely et al., 1991, Anal. Biochem. 194: 302-308), termed pT7-AAT constructs. HeLa cells are first infected with a recombinant vaccinia virus, VTF-7, that expresses T7 RNA polymerase. Cells are incubated with virus at a concentration of about 10 plaque-forming unit/cell in serum-free Dulbecco's modified Eagle's medium at 37° C. for 30 min., and then the cells were transfected with each of the amino acid transporter constructs described above (i.e. the pT7-AAT constructs) using a lipofectin-mediated (Bethesda Research Labs, Gaithersburg, Md.) transfection protocol (see Felgner et al., 1987, Proc. Natl. Acad. Sci. USA 84: 7413-7417). Cells are then incubated for 12-24 h before being assayed for amino acid transporter expression as described in Example 5.

EXAMPLE 9 Construction of Fusion Proteins-Recombinant Expression Constructs for Expression of Immunologically-Active Epitopes of Amino Acid Transporters

The amino acid transporter proteins of the invention are expressed as fusion proteins in bacteria to produce immunologically-active epitopes. In these experiments, each of the amino acid transporter cDNAs of the invention are excised from their respective pOTV-containing constructs and subcloned into a pGEX-2T construct (Pharmacia, Piscataway, N.J.) whereby the coding sequences of the amino acid transporter cDNAs are translationally in-frame with sequences encoding glutathione-S-transferase (described in Arriza et al., 1992, J. Neurosci. 12: 4045-4055), termed PGST-AAT constructs. After introduction of the PGST-AAT constructs into bacterial cells (E. coli, strain D5α) using conventional techniques (see Sambrook et al., ibid.), fusion protein expression is induced with isopropyl-1-thio-β-D-galactopyranoside as described (Smith & Johnson, 1988, Gene 67: 31-40) and are purified using glutathione-Sepharose 4B (Pharmacia). Antibodies are then raised against each of the amino acid transporters of the invention by inoculation of rabbits with 300-500 μg of purified fusion protein in Freund's adjuvant (Grand Island Biological Co., Grand Island, N.Y.), said inoculation repeated approximately every 4 weeks. Sera are immunoaffinity-purified on columns of Affi-Gel 15 derivatized with purified fusion protein. After salt elution, such antibodies are neutralized, stabilized with bovine serum albumin at a final concentration of 1 mg/mL, dialyzed against PBS and assayed by immunoblotting using conventional techniques (Harlow & Lane, 1988, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.).

It should be understood that the foregoing disclosure emphasizes certain specific embodiments of the invention and that all modifications or alternatives equivalent thereto are within the spirit and scope of the invention as set forth in the appended claims.

TABLE I ASCT1 RNA-injected Water-injected Amino Acid (1 mM)* Oocytes** Oocytes** Alanine 18 ± 2 0.6 ± 0.1 Serine   20 ± 5.1 0.4 ± 0.1 Cysteine 19.2 ± 5.9 1.0 ± 0.3 *n = 5; **pmol/min per oocyte:

TABLE II Amino Acid* K_(m) (μM) I_(max)** Alanine 71 ± 14 (1.0) Serine 88 ± 11 1.2 ± 0.08 Cysteine 29 ± 6  1.0 ± 0.04 Threonine 137 ± 19  1.4 ± 0.03 Valine 390 ± 8  0.6 ± 0.11 NOTE: data is expressed as the mean of at least 5 determinations ± standard error. *All amino acids were the L-stereoisomer **I_(max) was determined by least squares fit to the equation:

 I=I_(max)×([S]/(K_(m)+[S])

 where I_(max) is the maximal current and K_(m) is the transport constant

TABLE III Glutamate uptake inhibition constants. Ki (in μM) determined for each transporter^(a) Compound EAAT1 EAAT2 EAAT3 THA (L-threo-β- 32 ± 8 19 ± 6 25 ± 5 hydroxyaspartate) PDC 79 ± 7  8 ± 2  61 ± 14 (L-trans-pyrrolidine- 2,4-dicarboxylate) SOS (L-Serine-O-sulfate) 107 ± 8  1157 ± 275 150 ± 52 DHK (Dihydrokainate) >1 mM 23 ± 6 >1 mM KAI (Kainate) >1 mM  59 ± 18 >1 mM L-cysteate 10 ± 3 10 ± 2 19 ± 9 L-cysteine sulfinic acid 14 ± 7  6 ± 1 17 ± 2 β-glutamate  297 ± 118 156 ± 37 307 ± 48 L-aspartate-β-hydroxymate 369 ± 70 184 ± 27 133 ± 34 ^(a)Under the assay conditions used ([S] << Km). the Ki value does not differ significantly from the measured IC50.

17 63 base pairs nucleic acid single linear cDNA 1 CTGRGCRATG AARATGGCAG CCAGGGCYTC ATACAGGGCT GTGCCRTCCA TGTTRATGGT 60 RGC 63 1680 base pairs nucleic acid single linear cDNA 5′UTR 1..30 CDS 31..1626 3′UTR 1626..1680 2 CACCTCTAGC TCGGAGCGGC GTGTAGCGCC ATG GAG AAG AGC AAC GAG ACC AAC 54 Met Glu Lys Ser Asn Glu Thr Asn 1 5 GGC TAC CTT GAC AGC GCT CAG GCG GGG CCT GCG GCC GGG CCC GGA GCT 102 Gly Tyr Leu Asp Ser Ala Gln Ala Gly Pro Ala Ala Gly Pro Gly Ala 10 15 20 CCG GGG ACC GCG GCG GGA CGC GCA CGG CGT TGC GCG CGC TTC CTG CGG 150 Pro Gly Thr Ala Ala Gly Arg Ala Arg Arg Cys Ala Arg Phe Leu Arg 25 30 35 40 CGC CAA GCG CTG GTG CTG CTC ACC GTG TCC GGG GTG CTG GCG GGC GCG 198 Arg Gln Ala Leu Val Leu Leu Thr Val Ser Gly Val Leu Ala Gly Ala 45 50 55 GGC CTG GGC GCG GCG TTG CGC GGG CTC AGC CTG AGC CGC ACG CAG GTC 246 Gly Leu Gly Ala Ala Leu Arg Gly Leu Ser Leu Ser Arg Thr Gln Val 60 65 70 ACC TAC CTG GCC TTC CCC GGC GAG ATG CTG CTC CGC ATG CTG CGC ATG 294 Thr Tyr Leu Ala Phe Pro Gly Glu Met Leu Leu Arg Met Leu Arg Met 75 80 85 ATC ATC CTG CCG CTG GTG GTC TGC AGC CTG GTG TCG GGC GCC GCC TCG 342 Ile Ile Leu Pro Leu Val Val Cys Ser Leu Val Ser Gly Ala Ala Ser 90 95 100 CTC GAT GCC AGC TGC CTC GGG CGT CTG GGC GGC ATC CGT GTC GCC TAC 390 Leu Asp Ala Ser Cys Leu Gly Arg Leu Gly Gly Ile Arg Val Ala Tyr 105 110 115 120 TTT GGC CTC ACC ACA CTG AGT GCC TCG GCG CTC GCC GTG GCC TTG GCG 438 Phe Gly Leu Thr Thr Leu Ser Ala Ser Ala Leu Ala Val Ala Leu Ala 125 130 135 TTC ATC ATC AAG CCA GGA TCC GGT GCG CAG ACC CTT CAG TCC AGC GAC 486 Phe Ile Ile Lys Pro Gly Ser Gly Ala Gln Thr Leu Gln Ser Ser Asp 140 145 150 CTG GGG CTG GAG GAC TCG GGG CCT CCT CCT GTC CCC AAA GAG ACG GTG 534 Leu Gly Leu Glu Asp Ser Gly Pro Pro Pro Val Pro Lys Glu Thr Val 155 160 165 GAC TCT TTC CTC GAC CTG GCC AGA AAC CTG TTT CCC TCC AAT CTT GTG 582 Asp Ser Phe Leu Asp Leu Ala Arg Asn Leu Phe Pro Ser Asn Leu Val 170 175 180 GTT GCA GCT TTC CGT ACG TAT GCA ACC GAT TAT AAA GTC GTG ACC CAG 630 Val Ala Ala Phe Arg Thr Tyr Ala Thr Asp Tyr Lys Val Val Thr Gln 185 190 195 200 AAC AGC AGC TCT GGA AAT GTA ACC CAT GAA AAG ATC CCC ATA GGC ACT 678 Asn Ser Ser Ser Gly Asn Val Thr His Glu Lys Ile Pro Ile Gly Thr 205 210 215 GAG ATA GAA GGG ATG AAC ATT TTA GGA TTG GTC CTG TTT GCT CTG GTG 726 Glu Ile Glu Gly Met Asn Ile Leu Gly Leu Val Leu Phe Ala Leu Val 220 225 230 TTA GGA GTG GCC TTA AAG AAA CTA GGC TCC GAA GGA GAA GAC CTC ATC 774 Leu Gly Val Ala Leu Lys Lys Leu Gly Ser Glu Gly Glu Asp Leu Ile 235 240 245 CGT TTC TTC AAT TCC CTC AAC GAG GCG ACG ATG GTG CTG GTG TCC TGG 822 Arg Phe Phe Asn Ser Leu Asn Glu Ala Thr Met Val Leu Val Ser Trp 250 255 260 ATT ATG TGG TAC GTA CCT GTG GGC ATC ATG TTC CTT GTT GGA AGC AAG 870 Ile Met Trp Tyr Val Pro Val Gly Ile Met Phe Leu Val Gly Ser Lys 265 270 275 280 ATC GTG GAA ATG AAA GAC ATC ATC GTG CTG GTG ACC AGC CTG GGG AAA 918 Ile Val Glu Met Lys Asp Ile Ile Val Leu Val Thr Ser Leu Gly Lys 285 290 295 TAC ATC TTC GCA TCT ATA TTG GGC CAT GTT ATT CAT GGA GGA ATT GTT 966 Tyr Ile Phe Ala Ser Ile Leu Gly His Val Ile His Gly Gly Ile Val 300 305 310 CTG CCA CTT ATT TAT TTT GTT TTC ACA CGA AAA AAC CCA TTC AGA TTC 1014 Leu Pro Leu Ile Tyr Phe Val Phe Thr Arg Lys Asn Pro Phe Arg Phe 315 320 325 CTC CTG GGC CTC CTC GCC CCA TTT GCG ACA GCA TTT GCT ACC TGC TCC 1062 Leu Leu Gly Leu Leu Ala Pro Phe Ala Thr Ala Phe Ala Thr Cys Ser 330 335 340 AGC TCA GCG ACC CTT CCC TCT ATG ATG AAG TGC ATT GAA GAG AAC AAT 1110 Ser Ser Ala Thr Leu Pro Ser Met Met Lys Cys Ile Glu Glu Asn Asn 345 350 355 360 GGT GTG GAC AAG AGG ATC AGC AGG TTT ATT CTC CCC ATC GGG GCC ACC 1158 Gly Val Asp Lys Arg Ile Ser Arg Phe Ile Leu Pro Ile Gly Ala Thr 365 370 375 GTG AAC ATG GAC GGA GCA GCC ATC TTC CAG TGT GTG GCC GCG GTG TTC 1206 Val Asn Met Asp Gly Ala Ala Ile Phe Gln Cys Val Ala Ala Val Phe 380 385 390 ATT GCG CAA CTC AAC AAC ATA GAG CTC AAC GCA GGA CAG ATT TTC ACC 1254 Ile Ala Gln Leu Asn Asn Ile Glu Leu Asn Ala Gly Gln Ile Phe Thr 395 400 405 ATT CTA GTG ACT GCC ACA GCG TCC AGT GTT GGA GCA GCA GGC GTG CCA 1302 Ile Leu Val Thr Ala Thr Ala Ser Ser Val Gly Ala Ala Gly Val Pro 410 415 420 GCT GGA GGG GTC CTC ACC ATT GCC ATT ATC CTG GAG GCC ATT GGG CTG 1350 Ala Gly Gly Val Leu Thr Ile Ala Ile Ile Leu Glu Ala Ile Gly Leu 425 430 435 440 CCT ACT CAT GAC CTG CCT CTG ATC CTG GCT GTG GAC TGG ATT GTG GAC 1398 Pro Thr His Asp Leu Pro Leu Ile Leu Ala Val Asp Trp Ile Val Asp 445 450 455 CGG ACC ACC ACG GTG GTG AAT GTG GAG GGG GAT GCC CTG GGT GCA GGC 1446 Arg Thr Thr Thr Val Val Asn Val Glu Gly Asp Ala Leu Gly Ala Gly 460 465 470 ATT CTC CAC CAC CTG AAT CAG AAG GCA ACA AAG AAA GGC GAG CAG GAA 1494 Ile Leu His His Leu Asn Gln Lys Ala Thr Lys Lys Gly Glu Gln Glu 475 480 485 CTT GCT GAG GTG AAA GTG GAA GCC ATC CCC AAC TGC AAG TCT GAG GAG 1542 Leu Ala Glu Val Lys Val Glu Ala Ile Pro Asn Cys Lys Ser Glu Glu 490 495 500 GAG ACA TCG CCC CTG GTG ACA CAC CAG AAC CCC GCT GGC CCC GTG GCC 1590 Glu Thr Ser Pro Leu Val Thr His Gln Asn Pro Ala Gly Pro Val Ala 505 510 515 520 AGT GCC CCA GAA CTG GAA TCC AAG GAG TCG GTT CTG TGATGGGGCT 1636 Ser Ala Pro Glu Leu Glu Ser Lys Glu Ser Val Leu 525 530 GGGCTTTGGG CTTGCCTGCC AGCAGTGATG TCCCACCCTG TTCA 1680 532 amino acids amino acid linear protein 3 Met Glu Lys Ser Asn Glu Thr Asn Gly Tyr Leu Asp Ser Ala Gln Ala 1 5 10 15 Gly Pro Ala Ala Gly Pro Gly Ala Pro Gly Thr Ala Ala Gly Arg Ala 20 25 30 Arg Arg Cys Ala Arg Phe Leu Arg Arg Gln Ala Leu Val Leu Leu Thr 35 40 45 Val Ser Gly Val Leu Ala Gly Ala Gly Leu Gly Ala Ala Leu Arg Gly 50 55 60 Leu Ser Leu Ser Arg Thr Gln Val Thr Tyr Leu Ala Phe Pro Gly Glu 65 70 75 80 Met Leu Leu Arg Met Leu Arg Met Ile Ile Leu Pro Leu Val Val Cys 85 90 95 Ser Leu Val Ser Gly Ala Ala Ser Leu Asp Ala Ser Cys Leu Gly Arg 100 105 110 Leu Gly Gly Ile Arg Val Ala Tyr Phe Gly Leu Thr Thr Leu Ser Ala 115 120 125 Ser Ala Leu Ala Val Ala Leu Ala Phe Ile Ile Lys Pro Gly Ser Gly 130 135 140 Ala Gln Thr Leu Gln Ser Ser Asp Leu Gly Leu Glu Asp Ser Gly Pro 145 150 155 160 Pro Pro Val Pro Lys Glu Thr Val Asp Ser Phe Leu Asp Leu Ala Arg 165 170 175 Asn Leu Phe Pro Ser Asn Leu Val Val Ala Ala Phe Arg Thr Tyr Ala 180 185 190 Thr Asp Tyr Lys Val Val Thr Gln Asn Ser Ser Ser Gly Asn Val Thr 195 200 205 His Glu Lys Ile Pro Ile Gly Thr Glu Ile Glu Gly Met Asn Ile Leu 210 215 220 Gly Leu Val Leu Phe Ala Leu Val Leu Gly Val Ala Leu Lys Lys Leu 225 230 235 240 Gly Ser Glu Gly Glu Asp Leu Ile Arg Phe Phe Asn Ser Leu Asn Glu 245 250 255 Ala Thr Met Val Leu Val Ser Trp Ile Met Trp Tyr Val Pro Val Gly 260 265 270 Ile Met Phe Leu Val Gly Ser Lys Ile Val Glu Met Lys Asp Ile Ile 275 280 285 Val Leu Val Thr Ser Leu Gly Lys Tyr Ile Phe Ala Ser Ile Leu Gly 290 295 300 His Val Ile His Gly Gly Ile Val Leu Pro Leu Ile Tyr Phe Val Phe 305 310 315 320 Thr Arg Lys Asn Pro Phe Arg Phe Leu Leu Gly Leu Leu Ala Pro Phe 325 330 335 Ala Thr Ala Phe Ala Thr Cys Ser Ser Ser Ala Thr Leu Pro Ser Met 340 345 350 Met Lys Cys Ile Glu Glu Asn Asn Gly Val Asp Lys Arg Ile Ser Arg 355 360 365 Phe Ile Leu Pro Ile Gly Ala Thr Val Asn Met Asp Gly Ala Ala Ile 370 375 380 Phe Gln Cys Val Ala Ala Val Phe Ile Ala Gln Leu Asn Asn Ile Glu 385 390 395 400 Leu Asn Ala Gly Gln Ile Phe Thr Ile Leu Val Thr Ala Thr Ala Ser 405 410 415 Ser Val Gly Ala Ala Gly Val Pro Ala Gly Gly Val Leu Thr Ile Ala 420 425 430 Ile Ile Leu Glu Ala Ile Gly Leu Pro Thr His Asp Leu Pro Leu Ile 435 440 445 Leu Ala Val Asp Trp Ile Val Asp Arg Thr Thr Thr Val Val Asn Val 450 455 460 Glu Gly Asp Ala Leu Gly Ala Gly Ile Leu His His Leu Asn Gln Lys 465 470 475 480 Ala Thr Lys Lys Gly Glu Gln Glu Leu Ala Glu Val Lys Val Glu Ala 485 490 495 Ile Pro Asn Cys Lys Ser Glu Glu Glu Thr Ser Pro Leu Val Thr His 500 505 510 Gln Asn Pro Ala Gly Pro Val Ala Ser Ala Pro Glu Leu Glu Ser Lys 515 520 525 Glu Ser Val Leu 530 1680 base pairs nucleic acid single linear cDNA 5′UTR 1..30 CDS 31..1656 3′UTR 1657..1680 4 AAAGAAGAGA CCCTCCTAGA AAAGTAAAAT ATG ACT AAA AGC AAT GGA GAA GAG 54 Met Thr Lys Ser Asn Gly Glu Glu 1 5 CCC AAG ATG GGG GGC AGG ATG GAG AGA TTC CAG CAG GGA GTC CGT AAA 102 Pro Lys Met Gly Gly Arg Met Glu Arg Phe Gln Gln Gly Val Arg Lys 10 15 20 CGC ACA CTT TTG GCC AAG AAG AAA GTG CAG AAC ATT ACA AAG GAG GTT 150 Arg Thr Leu Leu Ala Lys Lys Lys Val Gln Asn Ile Thr Lys Glu Val 25 30 35 40 GTT AAA AGT TAC CTG TTT CGG AAT GCT TTT GTG CTG CTC ACA GTC ACC 198 Val Lys Ser Tyr Leu Phe Arg Asn Ala Phe Val Leu Leu Thr Val Thr 45 50 55 GCT GTC ATT GTG GGT ACA ATC CTT GGA TTT ACC CTC CGA CCA TAC AGA 246 Ala Val Ile Val Gly Thr Ile Leu Gly Phe Thr Leu Arg Pro Tyr Arg 60 65 70 ATG AGC TAC CGG GAA GTC AAG TAC TTC TCC TTT CCT GGG GAA CTT CTG 294 Met Ser Tyr Arg Glu Val Lys Tyr Phe Ser Phe Pro Gly Glu Leu Leu 75 80 85 ATG AGG ATG TTA CAG ATG CTG GTC TTA CCA CTT ATC ATC TCC AGT CTT 342 Met Arg Met Leu Gln Met Leu Val Leu Pro Leu Ile Ile Ser Ser Leu 90 95 100 GTC ACA GGA ATG GCG GCG CTA GAT AGT AAG GCA TCA GGG AAG TGG GAA 390 Val Thr Gly Met Ala Ala Leu Asp Ser Lys Ala Ser Gly Lys Trp Glu 105 110 115 120 TGC GGA GCT GTA GTC TAT TAT ATG ACT ACC ACC ATC ATT GCT GTG GTG 438 Cys Gly Ala Val Val Tyr Tyr Met Thr Thr Thr Ile Ile Ala Val Val 125 130 135 ATT GGC ATA ATC ATT GTC ATC ATC ATC CAT CCT GGG AAG GGC ACA AAG 486 Ile Gly Ile Ile Ile Val Ile Ile Ile His Pro Gly Lys Gly Thr Lys 140 145 150 GAA AAC ATG CAC AGA GAA GGC AAA ATT GTA CGA GTG ACA GCT GCA GAT 534 Glu Asn Met His Arg Glu Gly Lys Ile Val Arg Val Thr Ala Ala Asp 155 160 165 GCC TTC CTG GAC TTG ATC AGG AAC ATG TTA AAT CCA AAT CTG GTA GAA 582 Ala Phe Leu Asp Leu Ile Arg Asn Met Leu Asn Pro Asn Leu Val Glu 170 175 180 GCC TGC TTT AAA CAG TTT AAA ACC AAC TAT GAG AAG AGA AGC TTT AAA 630 Ala Cys Phe Lys Gln Phe Lys Thr Asn Tyr Glu Lys Arg Ser Phe Lys 185 190 195 200 GTG CCC ATC CAG GCC AAC GAA ACG CTT GTG GGT GCT GTG ATA AAC AAT 678 Val Pro Ile Gln Ala Asn Glu Thr Leu Val Gly Ala Val Ile Asn Asn 205 210 215 GTG TCT GAG GCC ATG GAG ACT CTT ACC CGA ATC ACA GAG GAG CTG GTC 726 Val Ser Glu Ala Met Glu Thr Leu Thr Arg Ile Thr Glu Glu Leu Val 220 225 230 CCA GTT CCA GGA TCT GTG AAT GGA GTC AAT GCC CTG GGT CTA GTT GTC 774 Pro Val Pro Gly Ser Val Asn Gly Val Asn Ala Leu Gly Leu Val Val 235 240 245 TTC TCC ATG TGC TTC GGT TTT GTG ATT GGA AAC ATG AAG GAA CAG GGG 822 Phe Ser Met Cys Phe Gly Phe Val Ile Gly Asn Met Lys Glu Gln Gly 250 255 260 CAG GCC CTG AGA GAG TTC TTT GAT TCT CTT AAC GAA GCC ATC ATG AGA 870 Gln Ala Leu Arg Glu Phe Phe Asp Ser Leu Asn Glu Ala Ile Met Arg 265 270 275 280 CTG GTA GCA GTA ATA ATG TGG TAT GCC CCC GTG GGT ATT CTC TTC CTG 918 Leu Val Ala Val Ile Met Trp Tyr Ala Pro Val Gly Ile Leu Phe Leu 285 290 295 ATT GCT GGG AAG ATT GTG GAG ATG GAA GAC ATG GGT GTG ATT GGG GGG 966 Ile Ala Gly Lys Ile Val Glu Met Glu Asp Met Gly Val Ile Gly Gly 300 305 310 CAG CTT GCC ATG TAC ACC GTG ACT GTC ATT GTT GGC TTA CTC ATT CAC 1014 Gln Leu Ala Met Tyr Thr Val Thr Val Ile Val Gly Leu Leu Ile His 315 320 325 GCA GTC ATC GTC TTG CCA CTC CTC TAC TTC TTG GTA ACA CGG AAA AAC 1062 Ala Val Ile Val Leu Pro Leu Leu Tyr Phe Leu Val Thr Arg Lys Asn 330 335 340 CCT TGG GTT TTT ATT GGA GGG TTG CTG CAA GCA CTC ATC ACC GCT CTG 1110 Pro Trp Val Phe Ile Gly Gly Leu Leu Gln Ala Leu Ile Thr Ala Leu 345 350 355 360 GGG ACC TCT TCA AGT TCT GCC ACC CTA CCC ATC ACC TTC AAG TGC CTG 1158 Gly Thr Ser Ser Ser Ser Ala Thr Leu Pro Ile Thr Phe Lys Cys Leu 365 370 375 GAA GAG AAC AAT GGC GTG GAC AAG CGC GTC ACC AGA TTC GTG CTC CCC 1206 Glu Glu Asn Asn Gly Val Asp Lys Arg Val Thr Arg Phe Val Leu Pro 380 385 390 GTA GGA GCC ACC ATT AAC ATG GAT GGG ACT GCC CTC TAT GAG GCT TTG 1254 Val Gly Ala Thr Ile Asn Met Asp Gly Thr Ala Leu Tyr Glu Ala Leu 395 400 405 GCT GCC ATT TTC ATT GCT CAA GTT AAC AAC TTT GAA CTG AAC TTC GGA 1302 Ala Ala Ile Phe Ile Ala Gln Val Asn Asn Phe Glu Leu Asn Phe Gly 410 415 420 CAA ATT ATT ACA ATC AGC ATC ACA GCC ACA GCT GCC AGT ATT GGG GCA 1350 Gln Ile Ile Thr Ile Ser Ile Thr Ala Thr Ala Ala Ser Ile Gly Ala 425 430 435 440 GCT GGA ATT CCT CAG GCG GGC CTG GTC ACT ATG GTC ATT GTG CTG ACA 1398 Ala Gly Ile Pro Gln Ala Gly Leu Val Thr Met Val Ile Val Leu Thr 445 450 455 TCT GTC GGC CTG CCC ACT GAC GAC ATC ACG CTC ATC ATC GCG GTG GAC 1446 Ser Val Gly Leu Pro Thr Asp Asp Ile Thr Leu Ile Ile Ala Val Asp 460 465 470 TGG TTC TTG GAT CGC CTC CGG ACC ACC ACC AAC GTA CTG GGA GAC TCC 1494 Trp Phe Leu Asp Arg Leu Arg Thr Thr Thr Asn Val Leu Gly Asp Ser 475 480 485 CTG GGA GCT GGG ATT GTG GAG CAC TTG TCA CGA CAT GAA CTG AAG AAC 1542 Leu Gly Ala Gly Ile Val Glu His Leu Ser Arg His Glu Leu Lys Asn 490 495 500 AGA GAT GTT GAA ATG GGT AAC TCA GTG ATT GAA GAG AAT GAA ATG AAG 1590 Arg Asp Val Glu Met Gly Asn Ser Val Ile Glu Glu Asn Glu Met Lys 505 510 515 520 AAA CCA TAT CAA CTG ATT GCA CAG GAC AAT GAA ACT GAG AAA CCC ATC 1638 Lys Pro Tyr Gln Leu Ile Ala Gln Asp Asn Glu Thr Glu Lys Pro Ile 525 530 535 GAC AGT GAA ACC AAG ATG TAGACTAACA TAAAGAAACA CTTT 1680 Asp Ser Glu Thr Lys Met 540 542 amino acids amino acid linear protein 5 Met Thr Lys Ser Asn Gly Glu Glu Pro Lys Met Gly Gly Arg Met Glu 1 5 10 15 Arg Phe Gln Gln Gly Val Arg Lys Arg Thr Leu Leu Ala Lys Lys Lys 20 25 30 Val Gln Asn Ile Thr Lys Glu Val Val Lys Ser Tyr Leu Phe Arg Asn 35 40 45 Ala Phe Val Leu Leu Thr Val Thr Ala Val Ile Val Gly Thr Ile Leu 50 55 60 Gly Phe Thr Leu Arg Pro Tyr Arg Met Ser Tyr Arg Glu Val Lys Tyr 65 70 75 80 Phe Ser Phe Pro Gly Glu Leu Leu Met Arg Met Leu Gln Met Leu Val 85 90 95 Leu Pro Leu Ile Ile Ser Ser Leu Val Thr Gly Met Ala Ala Leu Asp 100 105 110 Ser Lys Ala Ser Gly Lys Trp Glu Cys Gly Ala Val Val Tyr Tyr Met 115 120 125 Thr Thr Thr Ile Ile Ala Val Val Ile Gly Ile Ile Ile Val Ile Ile 130 135 140 Ile His Pro Gly Lys Gly Thr Lys Glu Asn Met His Arg Glu Gly Lys 145 150 155 160 Ile Val Arg Val Thr Ala Ala Asp Ala Phe Leu Asp Leu Ile Arg Asn 165 170 175 Met Leu Asn Pro Asn Leu Val Glu Ala Cys Phe Lys Gln Phe Lys Thr 180 185 190 Asn Tyr Glu Lys Arg Ser Phe Lys Val Pro Ile Gln Ala Asn Glu Thr 195 200 205 Leu Val Gly Ala Val Ile Asn Asn Val Ser Glu Ala Met Glu Thr Leu 210 215 220 Thr Arg Ile Thr Glu Glu Leu Val Pro Val Pro Gly Ser Val Asn Gly 225 230 235 240 Val Asn Ala Leu Gly Leu Val Val Phe Ser Met Cys Phe Gly Phe Val 245 250 255 Ile Gly Asn Met Lys Glu Gln Gly Gln Ala Leu Arg Glu Phe Phe Asp 260 265 270 Ser Leu Asn Glu Ala Ile Met Arg Leu Val Ala Val Ile Met Trp Tyr 275 280 285 Ala Pro Val Gly Ile Leu Phe Leu Ile Ala Gly Lys Ile Val Glu Met 290 295 300 Glu Asp Met Gly Val Ile Gly Gly Gln Leu Ala Met Tyr Thr Val Thr 305 310 315 320 Val Ile Val Gly Leu Leu Ile His Ala Val Ile Val Leu Pro Leu Leu 325 330 335 Tyr Phe Leu Val Thr Arg Lys Asn Pro Trp Val Phe Ile Gly Gly Leu 340 345 350 Leu Gln Ala Leu Ile Thr Ala Leu Gly Thr Ser Ser Ser Ser Ala Thr 355 360 365 Leu Pro Ile Thr Phe Lys Cys Leu Glu Glu Asn Asn Gly Val Asp Lys 370 375 380 Arg Val Thr Arg Phe Val Leu Pro Val Gly Ala Thr Ile Asn Met Asp 385 390 395 400 Gly Thr Ala Leu Tyr Glu Ala Leu Ala Ala Ile Phe Ile Ala Gln Val 405 410 415 Asn Asn Phe Glu Leu Asn Phe Gly Gln Ile Ile Thr Ile Ser Ile Thr 420 425 430 Ala Thr Ala Ala Ser Ile Gly Ala Ala Gly Ile Pro Gln Ala Gly Leu 435 440 445 Val Thr Met Val Ile Val Leu Thr Ser Val Gly Leu Pro Thr Asp Asp 450 455 460 Ile Thr Leu Ile Ile Ala Val Asp Trp Phe Leu Asp Arg Leu Arg Thr 465 470 475 480 Thr Thr Asn Val Leu Gly Asp Ser Leu Gly Ala Gly Ile Val Glu His 485 490 495 Leu Ser Arg His Glu Leu Lys Asn Arg Asp Val Glu Met Gly Asn Ser 500 505 510 Val Ile Glu Glu Asn Glu Met Lys Lys Pro Tyr Gln Leu Ile Ala Gln 515 520 525 Asp Asn Glu Thr Glu Lys Pro Ile Asp Ser Glu Thr Lys Met 530 535 540 1800 base pairs nucleic acid single linear cDNA 5′UTR 1..33 CDS 34..1755 3′UTR 1756..1800 6 GATAGTGCTG AAGAGGAGGG GCGTTCCCAG ACC ATG GCA TCT ACG GAA GGT GCC 54 Met Ala Ser Thr Glu Gly Ala 1 5 AAC AAT ATG CCC AAG CAG GTG GAA GTG CGA ATG CCA GAC AGT CAT CTT 102 Asn Asn Met Pro Lys Gln Val Glu Val Arg Met Pro Asp Ser His Leu 10 15 20 GGC TCA GAG GAA CCC AAG CAC CGG CAC CTG GGC CTG CGC CTG TGT GAC 150 Gly Ser Glu Glu Pro Lys His Arg His Leu Gly Leu Arg Leu Cys Asp 25 30 35 AAG CTG GGG AAG AAT CTG CTG CTC ACC CTG ACG GTG TTT GGT GTC ATC 198 Lys Leu Gly Lys Asn Leu Leu Leu Thr Leu Thr Val Phe Gly Val Ile 40 45 50 55 CTG GGA GCA GTG TGT GGA GGG CTT CTT CGC TTG GCA TCT CCC ATC CAC 246 Leu Gly Ala Val Cys Gly Gly Leu Leu Arg Leu Ala Ser Pro Ile His 60 65 70 CCT GAT GTG GTT ATG TTA ATA GCC TTC CCA GGG GAT ATA CTC ATG AGG 294 Pro Asp Val Val Met Leu Ile Ala Phe Pro Gly Asp Ile Leu Met Arg 75 80 85 ATG CTA AAA ATG CTC ATT CTG GGT CTA ATC ATC TCC AGC TTA ATC ACA 342 Met Leu Lys Met Leu Ile Leu Gly Leu Ile Ile Ser Ser Leu Ile Thr 90 95 100 GGG TTG TCA GGC CTG GAT GCT AAG GCT AGT GGC CGC TTG GGC ACG AGA 390 Gly Leu Ser Gly Leu Asp Ala Lys Ala Ser Gly Arg Leu Gly Thr Arg 105 110 115 GCC ATG GTG TAT TAC ATG TCC ACG ACC ATC ATT GCT GCA GTA CTG GGG 438 Ala Met Val Tyr Tyr Met Ser Thr Thr Ile Ile Ala Ala Val Leu Gly 120 125 130 135 GTC ATT CTG GTC TTG GCT ATC CAT CCA GGC AAT CCC AAG CTC AAG AAG 486 Val Ile Leu Val Leu Ala Ile His Pro Gly Asn Pro Lys Leu Lys Lys 140 145 150 CAG CTG GGG CCT GGG AAG AAG AAT GAT GAA GTG TCC AGC CTG GAT GCC 534 Gln Leu Gly Pro Gly Lys Lys Asn Asp Glu Val Ser Ser Leu Asp Ala 155 160 165 TTC CTG GAC CTT ATT CGA AAT CTC TTC CCT GAA AAC CTT GTC CAA GCC 582 Phe Leu Asp Leu Ile Arg Asn Leu Phe Pro Glu Asn Leu Val Gln Ala 170 175 180 TGC TTT CAA CAG ATT CAA ACA GTG ACG AAG AAA GTC CTG GTT GCA CCA 630 Cys Phe Gln Gln Ile Gln Thr Val Thr Lys Lys Val Leu Val Ala Pro 185 190 195 CCG CCA GAC GAG GAG GCC AAC GCA ACC AGC GCT GAA GTC TCT CTG TTG 678 Pro Pro Asp Glu Glu Ala Asn Ala Thr Ser Ala Glu Val Ser Leu Leu 200 205 210 215 AAC GAG ACT GTG ACT GAG GTG CCG GAG GAG ACT AAG ATG GTT ATC AAG 726 Asn Glu Thr Val Thr Glu Val Pro Glu Glu Thr Lys Met Val Ile Lys 220 225 230 AAG GGC CTG GAG TTC AAG GAT GGG ATG AAC GTC TTA GGT CTG ATA GGG 774 Lys Gly Leu Glu Phe Lys Asp Gly Met Asn Val Leu Gly Leu Ile Gly 235 240 245 TTT TTC ATT GCT TTT GGC ATC GCT ATG GGG AAG ATG GGA GAT CAG GCC 822 Phe Phe Ile Ala Phe Gly Ile Ala Met Gly Lys Met Gly Asp Gln Ala 250 255 260 AAG CTG ATG GTG GAT TTC TTC AAC ATT TTG AAT GAG ATT GTA ATG AAG 870 Lys Leu Met Val Asp Phe Phe Asn Ile Leu Asn Glu Ile Val Met Lys 265 270 275 TTA GTG ATC ATG ATC ATG TGG TAC TCT CCC CTG GGT ATC GCC TGC CTG 918 Leu Val Ile Met Ile Met Trp Tyr Ser Pro Leu Gly Ile Ala Cys Leu 280 285 290 295 ATC TGT GGA AAG ATC ATT GCA ATC AAG GAC TTA GAA GTG GTT GCT AGG 966 Ile Cys Gly Lys Ile Ile Ala Ile Lys Asp Leu Glu Val Val Ala Arg 300 305 310 CAA CTG GGG ATG TAC ATG GTA ACA GTG ATC ATA GGC CTC ATC ATC CAC 1014 Gln Leu Gly Met Tyr Met Val Thr Val Ile Ile Gly Leu Ile Ile His 315 320 325 GGG GGC ATC TTT CTC CCC TTG ATT TAC TTT GTA GTG ACC AGG AAA AAC 1062 Gly Gly Ile Phe Leu Pro Leu Ile Tyr Phe Val Val Thr Arg Lys Asn 330 335 340 CCC TTC TCC CTT TTT GCT GGC ATT TTC CAA GCT TGG ATC ACT GCC CTG 1110 Pro Phe Ser Leu Phe Ala Gly Ile Phe Gln Ala Trp Ile Thr Ala Leu 345 350 355 GGC ACC GCT TCC AGT GCT GGA ACT TTG CCT GTC ACC TTT CGT TGC CTG 1158 Gly Thr Ala Ser Ser Ala Gly Thr Leu Pro Val Thr Phe Arg Cys Leu 360 365 370 375 GAA GAA AAT CTG GGG ATT GAT AAG CGT GTG ACT AGA TTC GTC CTT CCT 1206 Glu Glu Asn Leu Gly Ile Asp Lys Arg Val Thr Arg Phe Val Leu Pro 380 385 390 GTT GGA GCA ACC ATT AAC ATG GAT GGT ACA GCC CTT TAT GAA GCG GTG 1254 Val Gly Ala Thr Ile Asn Met Asp Gly Thr Ala Leu Tyr Glu Ala Val 395 400 405 GCC GCC ATC TTT ATA GCC CAA ATG AAT GGT GTT GTC CTG GAT GGA GGA 1302 Ala Ala Ile Phe Ile Ala Gln Met Asn Gly Val Val Leu Asp Gly Gly 410 415 420 CAG ATT GTG ACT GTA AGC CTC ACA GCC ACC CTG GCA AGC GTC GGC GCG 1350 Gln Ile Val Thr Val Ser Leu Thr Ala Thr Leu Ala Ser Val Gly Ala 425 430 435 GCC AGT ATC CCC AGT GCC GGG CTG GTC ACC ATG CTC CTC ATT CTG ACA 1398 Ala Ser Ile Pro Ser Ala Gly Leu Val Thr Met Leu Leu Ile Leu Thr 440 445 450 455 GCC GTG GGC CTG CCA ACA GAG GAC ATC AGC TTG CTG GTG GCT GTG GAC 1446 Ala Val Gly Leu Pro Thr Glu Asp Ile Ser Leu Leu Val Ala Val Asp 460 465 470 TGG CTG CTG GAC AGG ATG AGA ACT TCA GTC AAT GTT GTG GGT GAC TCT 1494 Trp Leu Leu Asp Arg Met Arg Thr Ser Val Asn Val Val Gly Asp Ser 475 480 485 TTT GGG GCT GGG ATA GTC TAT CAC CTC TCC AAG TCT GAG CTG GAT ACC 1542 Phe Gly Ala Gly Ile Val Tyr His Leu Ser Lys Ser Glu Leu Asp Thr 490 495 500 ATT GAC TCC CAG CAT CGA GTG CAT GAA GAT ATT GAA ATG ACC AAG ACT 1590 Ile Asp Ser Gln His Arg Val His Glu Asp Ile Glu Met Thr Lys Thr 505 510 515 CAA TCC ATT TAT GAT GAC ATG AAG AAC CAC AGG GAA AGC AAC TCT AAT 1638 Gln Ser Ile Tyr Asp Asp Met Lys Asn His Arg Glu Ser Asn Ser Asn 520 525 530 535 CAA TGT GTC TAT GCT GCA CAC AAC TCT GTC ATA GTA GAT GAA TGC AAG 1686 Gln Cys Val Tyr Ala Ala His Asn Ser Val Ile Val Asp Glu Cys Lys 540 545 550 GTA ACT CTG GCA GCC AAT GGA AAG TCA GCC GAC TGC AGT GTT GAG GAA 1734 Val Thr Leu Ala Ala Asn Gly Lys Ser Ala Asp Cys Ser Val Glu Glu 555 560 565 GAA CCT TGG AAA CGT GAG AAA TAAGGATATG AGTCTCAGCA AATTCTTGAA 1785 Glu Pro Trp Lys Arg Glu Lys 570 TAAACTCCCC AGCGT 1800 574 amino acids amino acid linear protein 7 Met Ala Ser Thr Glu Gly Ala Asn Asn Met Pro Lys Gln Val Glu Val 1 5 10 15 Arg Met Pro Asp Ser His Leu Gly Ser Glu Glu Pro Lys His Arg His 20 25 30 Leu Gly Leu Arg Leu Cys Asp Lys Leu Gly Lys Asn Leu Leu Leu Thr 35 40 45 Leu Thr Val Phe Gly Val Ile Leu Gly Ala Val Cys Gly Gly Leu Leu 50 55 60 Arg Leu Ala Ser Pro Ile His Pro Asp Val Val Met Leu Ile Ala Phe 65 70 75 80 Pro Gly Asp Ile Leu Met Arg Met Leu Lys Met Leu Ile Leu Gly Leu 85 90 95 Ile Ile Ser Ser Leu Ile Thr Gly Leu Ser Gly Leu Asp Ala Lys Ala 100 105 110 Ser Gly Arg Leu Gly Thr Arg Ala Met Val Tyr Tyr Met Ser Thr Thr 115 120 125 Ile Ile Ala Ala Val Leu Gly Val Ile Leu Val Leu Ala Ile His Pro 130 135 140 Gly Asn Pro Lys Leu Lys Lys Gln Leu Gly Pro Gly Lys Lys Asn Asp 145 150 155 160 Glu Val Ser Ser Leu Asp Ala Phe Leu Asp Leu Ile Arg Asn Leu Phe 165 170 175 Pro Glu Asn Leu Val Gln Ala Cys Phe Gln Gln Ile Gln Thr Val Thr 180 185 190 Lys Lys Val Leu Val Ala Pro Pro Pro Asp Glu Glu Ala Asn Ala Thr 195 200 205 Ser Ala Glu Val Ser Leu Leu Asn Glu Thr Val Thr Glu Val Pro Glu 210 215 220 Glu Thr Lys Met Val Ile Lys Lys Gly Leu Glu Phe Lys Asp Gly Met 225 230 235 240 Asn Val Leu Gly Leu Ile Gly Phe Phe Ile Ala Phe Gly Ile Ala Met 245 250 255 Gly Lys Met Gly Asp Gln Ala Lys Leu Met Val Asp Phe Phe Asn Ile 260 265 270 Leu Asn Glu Ile Val Met Lys Leu Val Ile Met Ile Met Trp Tyr Ser 275 280 285 Pro Leu Gly Ile Ala Cys Leu Ile Cys Gly Lys Ile Ile Ala Ile Lys 290 295 300 Asp Leu Glu Val Val Ala Arg Gln Leu Gly Met Tyr Met Val Thr Val 305 310 315 320 Ile Ile Gly Leu Ile Ile His Gly Gly Ile Phe Leu Pro Leu Ile Tyr 325 330 335 Phe Val Val Thr Arg Lys Asn Pro Phe Ser Leu Phe Ala Gly Ile Phe 340 345 350 Gln Ala Trp Ile Thr Ala Leu Gly Thr Ala Ser Ser Ala Gly Thr Leu 355 360 365 Pro Val Thr Phe Arg Cys Leu Glu Glu Asn Leu Gly Ile Asp Lys Arg 370 375 380 Val Thr Arg Phe Val Leu Pro Val Gly Ala Thr Ile Asn Met Asp Gly 385 390 395 400 Thr Ala Leu Tyr Glu Ala Val Ala Ala Ile Phe Ile Ala Gln Met Asn 405 410 415 Gly Val Val Leu Asp Gly Gly Gln Ile Val Thr Val Ser Leu Thr Ala 420 425 430 Thr Leu Ala Ser Val Gly Ala Ala Ser Ile Pro Ser Ala Gly Leu Val 435 440 445 Thr Met Leu Leu Ile Leu Thr Ala Val Gly Leu Pro Thr Glu Asp Ile 450 455 460 Ser Leu Leu Val Ala Val Asp Trp Leu Leu Asp Arg Met Arg Thr Ser 465 470 475 480 Val Asn Val Val Gly Asp Ser Phe Gly Ala Gly Ile Val Tyr His Leu 485 490 495 Ser Lys Ser Glu Leu Asp Thr Ile Asp Ser Gln His Arg Val His Glu 500 505 510 Asp Ile Glu Met Thr Lys Thr Gln Ser Ile Tyr Asp Asp Met Lys Asn 515 520 525 His Arg Glu Ser Asn Ser Asn Gln Cys Val Tyr Ala Ala His Asn Ser 530 535 540 Val Ile Val Asp Glu Cys Lys Val Thr Leu Ala Ala Asn Gly Lys Ser 545 550 555 560 Ala Asp Cys Ser Val Glu Glu Glu Pro Trp Lys Arg Glu Lys 565 570 1674 base pairs nucleic acid single linear cDNA 5′UTR 1..15 CDS 16..1590 3′UTR 1591..1674 8 ATAGCGGCGA CAGCC ATG GGG AAA CCG GCG AGG AAA GGA TGC CCG AGT TGG 51 Met Gly Lys Pro Ala Arg Lys Gly Cys Pro Ser Trp 1 5 10 AAG CGC TTC CTG AAG AAT AAC TGG GTG TTG CTG TCC ACC GTG GCC GCG 99 Lys Arg Phe Leu Lys Asn Asn Trp Val Leu Leu Ser Thr Val Ala Ala 15 20 25 GTG GTG CTA GGC ATT ACC ACA GGA GTC TTG GTT CGA GAA CAC AGC AAC 147 Val Val Leu Gly Ile Thr Thr Gly Val Leu Val Arg Glu His Ser Asn 30 35 40 CTC TCA ACT CTA GAG AAA TTC TAC TTT GCT TTT CCT GGA GAA ATT CTA 195 Leu Ser Thr Leu Glu Lys Phe Tyr Phe Ala Phe Pro Gly Glu Ile Leu 45 50 55 60 ATG CGG ATG CTG AAA CTC ATC ATT TTG CCA TTA ATT ATA TCC AGC ATG 243 Met Arg Met Leu Lys Leu Ile Ile Leu Pro Leu Ile Ile Ser Ser Met 65 70 75 ATT ACA GGT GTT GCT GCA CTG GAT TCC AAC GTA TCC GGA AAA ATT GGT 291 Ile Thr Gly Val Ala Ala Leu Asp Ser Asn Val Ser Gly Lys Ile Gly 80 85 90 CTG CGC GCT GTC GTG TAT TAT TTC TGT ACC ACT CTC ATT GCT GTT ATT 339 Leu Arg Ala Val Val Tyr Tyr Phe Cys Thr Thr Leu Ile Ala Val Ile 95 100 105 CTA GGT ATT GTG CTG GTG GTG AGC ATC AAG CCT GGT GTC ACC CAG AAA 387 Leu Gly Ile Val Leu Val Val Ser Ile Lys Pro Gly Val Thr Gln Lys 110 115 120 GTG GGT GAA ATT GCG AGG ACA GGC AGC ACC CCT GAA GTC AGT ACG GTG 435 Val Gly Glu Ile Ala Arg Thr Gly Ser Thr Pro Glu Val Ser Thr Val 125 130 135 140 GAT GCC ATG TTA GAT CTC ATC AGG AAT ATG TTC CCT GAG AAT CTT GTC 483 Asp Ala Met Leu Asp Leu Ile Arg Asn Met Phe Pro Glu Asn Leu Val 145 150 155 CAG GCC TGT TTT CAG CAG TAC AAA ACT AAG CGT GAA GAA GTG AAG CCT 531 Gln Ala Cys Phe Gln Gln Tyr Lys Thr Lys Arg Glu Glu Val Lys Pro 160 165 170 CCC AGC GAT CCA GAG ATG AAC ATG ACA GAA GAG TCC TTC ACA GCT GTC 579 Pro Ser Asp Pro Glu Met Asn Met Thr Glu Glu Ser Phe Thr Ala Val 175 180 185 ATG ACA ACT GCA ATT TCC AAG AAC AAA ACA AAG GAA TAC AAA ATT GTT 627 Met Thr Thr Ala Ile Ser Lys Asn Lys Thr Lys Glu Tyr Lys Ile Val 190 195 200 GGC ATG TAT TCA GAT GGC ATA AAC GTC CTG GGC TTG ATT GTC TTT TGC 675 Gly Met Tyr Ser Asp Gly Ile Asn Val Leu Gly Leu Ile Val Phe Cys 205 210 215 220 CTT GTC TTT GGA CTT GTC ATT GGA AAA ATG GGA GAA AAG GGA CAA ATT 723 Leu Val Phe Gly Leu Val Ile Gly Lys Met Gly Glu Lys Gly Gln Ile 225 230 235 CTG GTG GAT TTC TTC AAT GCT TTG AGT GAT GCA ACC ATG AAA ATC GTT 771 Leu Val Asp Phe Phe Asn Ala Leu Ser Asp Ala Thr Met Lys Ile Val 240 245 250 CAG ATC ATC ATG TGT TAT ATG CCA CTA GGT ATT TTG TTC CTG ATT GCT 819 Gln Ile Ile Met Cys Tyr Met Pro Leu Gly Ile Leu Phe Leu Ile Ala 255 260 265 GGG AAG ATC ATA GAA GTT GAA GAC TGG GAA ATA TTC CGC AAG CTG GGC 867 Gly Lys Ile Ile Glu Val Glu Asp Trp Glu Ile Phe Arg Lys Leu Gly 270 275 280 CTT TAC ATG GCC ACA GTC CTG ACT GGG CTT GCA ATC CAC TCC ATT GTA 915 Leu Tyr Met Ala Thr Val Leu Thr Gly Leu Ala Ile His Ser Ile Val 285 290 295 300 ATT CTC CCG CTG ATA TAT TTC ATA GTC GTA CGA AAG AAC CCT TTC CGA 963 Ile Leu Pro Leu Ile Tyr Phe Ile Val Val Arg Lys Asn Pro Phe Arg 305 310 315 TTT GCC ATG GGA ATG GCC CAG GCT CTC CTG ACA GCT CTC ATG ATC TCT 1011 Phe Ala Met Gly Met Ala Gln Ala Leu Leu Thr Ala Leu Met Ile Ser 320 325 330 TCC AGT TCA GCA ACA CTG CCT GTC ACC TTC CGC TGT GCT GAA GAA AAT 1059 Ser Ser Ser Ala Thr Leu Pro Val Thr Phe Arg Cys Ala Glu Glu Asn 335 340 345 AAC CAG GTG GAC AAG AGG ATC ACT CGA TTC GTG TTA CCC GTT GGT GCA 1107 Asn Gln Val Asp Lys Arg Ile Thr Arg Phe Val Leu Pro Val Gly Ala 350 355 360 ACA ATC AAC ATG GAT GGG ACC GCG CTC TAT GAA GCA GTG GCA GCG GTG 1155 Thr Ile Asn Met Asp Gly Thr Ala Leu Tyr Glu Ala Val Ala Ala Val 365 370 375 380 TTT ATT GCA CAG TTG AAT GAC CTG GAC TTG GGC ATT GGG CAG ATC ATC 1203 Phe Ile Ala Gln Leu Asn Asp Leu Asp Leu Gly Ile Gly Gln Ile Ile 385 390 395 ACC ATC AGT ATC ACG GCC ACA TCT GCC AGC ATC GGA GCT GCT GGC GTG 1251 Thr Ile Ser Ile Thr Ala Thr Ser Ala Ser Ile Gly Ala Ala Gly Val 400 405 410 CCC CAG GCT GGC CTG GTG ACC ATG GTG ATT GTG CTG AGT GCC GTG GGC 1299 Pro Gln Ala Gly Leu Val Thr Met Val Ile Val Leu Ser Ala Val Gly 415 420 425 CTG CCC GCC GAG GAT GTC ACC CTG ATC ATT GCT GTC GAC TGG CTC CTG 1347 Leu Pro Ala Glu Asp Val Thr Leu Ile Ile Ala Val Asp Trp Leu Leu 430 435 440 GAC CGG TTC AGG ACC ATG GTC AAC GTC CTT GGT GAT GCT TTT GGG ACG 1395 Asp Arg Phe Arg Thr Met Val Asn Val Leu Gly Asp Ala Phe Gly Thr 445 450 455 460 GGC ATT GTG GAA AAG CTC TCC AAG AAG GAG CTG GAG CAG ATG GAT GTT 1443 Gly Ile Val Glu Lys Leu Ser Lys Lys Glu Leu Glu Gln Met Asp Val 465 470 475 TCA TCT GAA GTC AAC ATT GTG AAT CCC TTT GCC TTG GAA TCC ACA ATC 1491 Ser Ser Glu Val Asn Ile Val Asn Pro Phe Ala Leu Glu Ser Thr Ile 480 485 490 CTT GAC AAC GAA GAC TCA GAC ACC AAG AAG TCT TAT GTC AAT GGA GGC 1539 Leu Asp Asn Glu Asp Ser Asp Thr Lys Lys Ser Tyr Val Asn Gly Gly 495 500 505 TTT GCA GTA GAC AAG TCT GAC ACC ATC TCA TTC ACC CAG ACC TCA CAG 1587 Phe Ala Val Asp Lys Ser Asp Thr Ile Ser Phe Thr Gln Thr Ser Gln 510 515 520 TTC TAGGGCCCCT GGCTGCAGAT GACTGGAAAC AAGGAAGGAC ATTTCGTGAG 1640 Phe 525 AGTCATCTCA AACACGGCTT AAGGAAAAGA GAAA 1674 525 amino acids amino acid linear protein 9 Met Gly Lys Pro Ala Arg Lys Gly Cys Pro Ser Trp Lys Arg Phe Leu 1 5 10 15 Lys Asn Asn Trp Val Leu Leu Ser Thr Val Ala Ala Val Val Leu Gly 20 25 30 Ile Thr Thr Gly Val Leu Val Arg Glu His Ser Asn Leu Ser Thr Leu 35 40 45 Glu Lys Phe Tyr Phe Ala Phe Pro Gly Glu Ile Leu Met Arg Met Leu 50 55 60 Lys Leu Ile Ile Leu Pro Leu Ile Ile Ser Ser Met Ile Thr Gly Val 65 70 75 80 Ala Ala Leu Asp Ser Asn Val Ser Gly Lys Ile Gly Leu Arg Ala Val 85 90 95 Val Tyr Tyr Phe Cys Thr Thr Leu Ile Ala Val Ile Leu Gly Ile Val 100 105 110 Leu Val Val Ser Ile Lys Pro Gly Val Thr Gln Lys Val Gly Glu Ile 115 120 125 Ala Arg Thr Gly Ser Thr Pro Glu Val Ser Thr Val Asp Ala Met Leu 130 135 140 Asp Leu Ile Arg Asn Met Phe Pro Glu Asn Leu Val Gln Ala Cys Phe 145 150 155 160 Gln Gln Tyr Lys Thr Lys Arg Glu Glu Val Lys Pro Pro Ser Asp Pro 165 170 175 Glu Met Asn Met Thr Glu Glu Ser Phe Thr Ala Val Met Thr Thr Ala 180 185 190 Ile Ser Lys Asn Lys Thr Lys Glu Tyr Lys Ile Val Gly Met Tyr Ser 195 200 205 Asp Gly Ile Asn Val Leu Gly Leu Ile Val Phe Cys Leu Val Phe Gly 210 215 220 Leu Val Ile Gly Lys Met Gly Glu Lys Gly Gln Ile Leu Val Asp Phe 225 230 235 240 Phe Asn Ala Leu Ser Asp Ala Thr Met Lys Ile Val Gln Ile Ile Met 245 250 255 Cys Tyr Met Pro Leu Gly Ile Leu Phe Leu Ile Ala Gly Lys Ile Ile 260 265 270 Glu Val Glu Asp Trp Glu Ile Phe Arg Lys Leu Gly Leu Tyr Met Ala 275 280 285 Thr Val Leu Thr Gly Leu Ala Ile His Ser Ile Val Ile Leu Pro Leu 290 295 300 Ile Tyr Phe Ile Val Val Arg Lys Asn Pro Phe Arg Phe Ala Met Gly 305 310 315 320 Met Ala Gln Ala Leu Leu Thr Ala Leu Met Ile Ser Ser Ser Ser Ala 325 330 335 Thr Leu Pro Val Thr Phe Arg Cys Ala Glu Glu Asn Asn Gln Val Asp 340 345 350 Lys Arg Ile Thr Arg Phe Val Leu Pro Val Gly Ala Thr Ile Asn Met 355 360 365 Asp Gly Thr Ala Leu Tyr Glu Ala Val Ala Ala Val Phe Ile Ala Gln 370 375 380 Leu Asn Asp Leu Asp Leu Gly Ile Gly Gln Ile Ile Thr Ile Ser Ile 385 390 395 400 Thr Ala Thr Ser Ala Ser Ile Gly Ala Ala Gly Val Pro Gln Ala Gly 405 410 415 Leu Val Thr Met Val Ile Val Leu Ser Ala Val Gly Leu Pro Ala Glu 420 425 430 Asp Val Thr Leu Ile Ile Ala Val Asp Trp Leu Leu Asp Arg Phe Arg 435 440 445 Thr Met Val Asn Val Leu Gly Asp Ala Phe Gly Thr Gly Ile Val Glu 450 455 460 Lys Leu Ser Lys Lys Glu Leu Glu Gln Met Asp Val Ser Ser Glu Val 465 470 475 480 Asn Ile Val Asn Pro Phe Ala Leu Glu Ser Thr Ile Leu Asp Asn Glu 485 490 495 Asp Ser Asp Thr Lys Lys Ser Tyr Val Asn Gly Gly Phe Ala Val Asp 500 505 510 Lys Ser Asp Thr Ile Ser Phe Thr Gln Thr Ser Gln Phe 515 520 525 28 base pairs nucleic acid single linear DNA (genomic) 10 CGCGGGTACC GCCATGGAGA AGAGCAAC 28 29 base pairs nucleic acid single linear DNA (genomic) 11 CGCGTCTAGA TCACAGAACC GACTCCTTG 29 29 base pairs nucleic acid single linear DNA (genomic) 12 CGCGGGTACC AATATGACTA AAAGCAATG 29 29 base pairs nucleic acid single linear DNA (genomic) 13 CGCGTCTAGA CTACATCTTG GTTTCACTG 29 29 base pairs nucleic acid single linear DNA (genomic) 14 CGCGGGTACC ACCATGGCAT CTACGGAAG 29 30 base pairs nucleic acid single linear DNA (genomic) 15 CGCGTCTAGA TTATTTCTCA CGTTTCCAAG 30 28 base pairs nucleic acid single linear DNA (genomic) 16 CGCGGGTACC GCCATGGGGA AACCGGCG 28 28 base pairs nucleic acid single linear DNA (genomic) 17 CGCGGGATCC CTAGAACTGT GAGGTCTG 28 

What is claimed is:
 1. An isolated 62.1 kilodalton human excitatory amino acid transporter produced by expressing in a cell a recombinant expression vector encoding human EAAT2.
 2. The human excitatory amino acid transporter of claim 1 having an amino acid sequence identified as SEQ ID No.:7.
 3. A cell membrane preparation comprising a 62.1 kilodalton human excitatory amino acid transporter that is EAAT2, produced by a cell that expresses a recombinant expression vector encoding human EAAT2.
 4. The cell membrane preparation of claim 3, wherein the human excitatory amino acid transporter has an amino acid sequence identified as SEQ ID No.:
 7. 